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 $176.71   13.346%   $200.2937   $200.29   $200.30   $200.30  
  Purchase #2 $103.35   9.735%   $113.4111   $113.41   $113.40   $113.40  
  Purchase #3 $116.33   8.635%   $126.3751   $126.38   $126.40   $126.40  
  Purchase #4 $92.59   7.447%   $99.4852   $99.49   $99.50   $99.50  
  Purchase #5 $186.65   5.610%   $197.1211   $197.12   $197.10   $197.10  
  Purchase #6 $169.76   10.332%   $187.2996   $187.30   $187.30   $187.30  
  Purchase #7 $109.82   3.399%   $113.5528   $113.55   $113.55   $113.60  
  7 purchase totals = $955.21       $1,037.5386   $1,037.54   $1,037.55   $1,037.60