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 $152.54   12.219%   $171.1789   $171.18   $171.20   $171.20  
  Purchase #2 $211.60   13.683%   $240.5532   $240.55   $240.55   $240.60  
  Purchase #3 $13.36   3.469%   $13.8235   $13.82   $13.80   $13.80  
  Purchase #4 $94.32   5.395%   $99.4086   $99.41   $99.40   $99.40  
  Purchase #5 $96.42   9.213%   $105.3032   $105.30   $105.30   $105.30  
  Purchase #6 $238.38   4.361%   $248.7758   $248.78   $248.80   $248.80  
  Purchase #7 $15.57   11.106%   $17.2992   $17.30   $17.30   $17.30  
  7 purchase totals = $822.19       $896.3424   $896.34   $896.35   $896.40