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 $62.82   6.115%   $66.6614   $66.66   $66.65   $66.70  
  Purchase #2 $182.39   13.685%   $207.3501   $207.35   $207.35   $207.40  
  Purchase #3 $94.87   3.361%   $98.0586   $98.06   $98.05   $98.10  
  Purchase #4 $129.51   6.499%   $137.9269   $137.93   $137.95   $137.90  
  Purchase #5 $237.47   12.229%   $266.5102   $266.51   $266.50   $266.50  
  Purchase #6 $43.35   11.649%   $48.3998   $48.40   $48.40   $48.40  
  Purchase #7 $64.56   6.863%   $68.9908   $68.99   $69.00   $69.00  
  7 purchase totals = $814.97       $893.8978   $893.90   $893.90   $894.00