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 $56.85   11.532%   $63.4059   $63.41   $63.40   $63.40  
  Purchase #2 $201.44   7.713%   $216.9771   $216.98   $217.00   $217.00  
  Purchase #3 $148.88   7.174%   $159.5607   $159.56   $159.55   $159.60  
  Purchase #4 $109.25   3.637%   $113.2234   $113.22   $113.20   $113.20  
  Purchase #5 $133.48   9.618%   $146.3181   $146.32   $146.30   $146.30  
  Purchase #6 $49.68   3.110%   $51.225   $51.23   $51.25   $51.20  
  Purchase #7 $60.69   10.765%   $67.2233   $67.22   $67.20   $67.20  
  7 purchase totals = $760.27       $817.9335   $817.94   $817.90   $817.90