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 $46.95   3.498%   $48.5923   $48.59   $48.60   $48.60  
  Purchase #2 $135.63   4.180%   $141.2993   $141.30   $141.30   $141.30  
  Purchase #3 $141.54   12.780%   $159.6288   $159.63   $159.65   $159.60  
  Purchase #4 $52.93   6.865%   $56.5636   $56.56   $56.55   $56.60  
  Purchase #5 $149.34   9.793%   $163.9649   $163.96   $163.95   $164.00  
  Purchase #6 $86.70   9.559%   $94.9877   $94.99   $95.00   $95.00  
  Purchase #7 $161.83   10.828%   $179.353   $179.35   $179.35   $179.40  
  7 purchase totals = $774.92       $844.3896   $844.38   $844.40   $844.50