Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $219.63   12.613%   $247.3319   $247.33   $247.35   $247.30  
  Purchase #2 $203.53   10.547%   $224.9963   $225.00   $225.00   $225.00  
  Purchase #3 $206.53   11.826%   $230.9542   $230.95   $230.95   $231.00  
  Purchase #4 $120.37   12.316%   $135.1948   $135.19   $135.20   $135.20  
  Purchase #5 $189.43   11.567%   $211.3414   $211.34   $211.35   $211.30  
  Purchase #6 $151.74   3.359%   $156.8369   $156.84   $156.85   $156.80  
  Purchase #7 $245.45   4.174%   $255.6951   $255.70   $255.70   $255.70  
  7 purchase totals = $1,336.68       $1,462.3506   $1,462.35   $1,462.40   $1,462.30