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 $57.63   10.748%   $63.8241   $63.82   $63.80   $63.80  
  Purchase #2 $170.39   13.412%   $193.2427   $193.24   $193.25   $193.20  
  Purchase #3 $88.44   11.206%   $98.3506   $98.35   $98.35   $98.40  
  Purchase #4 $150.51   6.471%   $160.2495   $160.25   $160.25   $160.20  
  Purchase #5 $135.76   12.275%   $152.4245   $152.42   $152.40   $152.40  
  Purchase #6 $41.71   11.465%   $46.4921   $46.49   $46.50   $46.50  
  Purchase #7 $34.37   9.134%   $37.5094   $37.51   $37.50   $37.50  
  7 purchase totals = $678.81       $752.0929   $752.08   $752.05   $752.00