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 $219.99   12.699%   $247.9265   $247.93   $247.95   $247.90  
  Purchase #2 $145.39   10.461%   $160.5992   $160.60   $160.60   $160.60  
  Purchase #3 $239.65   8.237%   $259.39   $259.39   $259.40   $259.40  
  Purchase #4 $70.99   11.623%   $79.2412   $79.24   $79.25   $79.20  
  Purchase #5 $30.57   4.689%   $32.0034   $32.00   $32.00   $32.00  
  Purchase #6 $226.59   13.544%   $257.2793   $257.28   $257.30   $257.30  
  Purchase #7 $158.29   6.612%   $168.7561   $168.76   $168.75   $168.80  
  7 purchase totals = $1,091.47       $1,205.1957   $1,205.20   $1,205.25   $1,205.20