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 $206.27   13.198%   $233.4935   $233.49   $233.50   $233.50  
  Purchase #2 $215.48   9.192%   $235.2869   $235.29   $235.30   $235.30  
  Purchase #3 $177.70   13.754%   $202.1409   $202.14   $202.15   $202.10  
  Purchase #4 $170.44   9.317%   $186.3199   $186.32   $186.30   $186.30  
  Purchase #5 $147.66   11.210%   $164.2127   $164.21   $164.20   $164.20  
  Purchase #6 $244.37   13.316%   $276.9103   $276.91   $276.90   $276.90  
  Purchase #7 $35.49   11.574%   $39.5976   $39.60   $39.60   $39.60  
  7 purchase totals = $1,197.41       $1,337.9618   $1,337.96   $1,337.95   $1,337.90