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 $56.92   11.530%   $63.4829   $63.48   $63.50   $63.50  
  Purchase #2 $178.91   13.597%   $203.2364   $203.24   $203.25   $203.20  
  Purchase #3 $49.54   6.703%   $52.8607   $52.86   $52.85   $52.90  
  Purchase #4 $178.99   11.777%   $200.0697   $200.07   $200.05   $200.10  
  Purchase #5 $84.50   10.405%   $93.2922   $93.29   $93.30   $93.30  
  Purchase #6 $79.72   5.637%   $84.2138   $84.21   $84.20   $84.20  
  Purchase #7 $223.34   6.478%   $237.808   $237.81   $237.80   $237.80  
  7 purchase totals = $851.92       $934.9637   $934.96   $934.95   $935.00