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 $56.70   11.571%   $63.2608   $63.26   $63.25   $63.30  
  Purchase #2 $88.25   6.326%   $93.8327   $93.83   $93.85   $93.80  
  Purchase #3 $92.41   11.162%   $102.7248   $102.72   $102.70   $102.70  
  Purchase #4 $184.43   8.108%   $199.3836   $199.38   $199.40   $199.40  
  Purchase #5 $90.42   11.237%   $100.5805   $100.58   $100.60   $100.60  
  Purchase #6 $171.79   13.335%   $194.6982   $194.70   $194.70   $194.70  
  Purchase #7 $48.84   5.486%   $51.5194   $51.52   $51.50   $51.50  
  7 purchase totals = $732.84       $806.0000   $805.99   $806.00   $806.00