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 $53.75   11.753%   $60.0672   $60.07   $60.05   $60.10  
  Purchase #2 $239.84   13.744%   $272.8036   $272.80   $272.80   $272.80  
  Purchase #3 $129.63   8.281%   $140.3647   $140.36   $140.35   $140.40  
  Purchase #4 $81.89   9.229%   $89.4476   $89.45   $89.45   $89.40  
  Purchase #5 $240.83   8.486%   $261.2668   $261.27   $261.25   $261.30  
  Purchase #6 $42.55   5.650%   $44.9541   $44.95   $44.95   $45.00  
  Purchase #7 $169.67   12.365%   $190.6497   $190.65   $190.65   $190.60  
  7 purchase totals = $958.16       $1,059.5537   $1,059.55   $1,059.50   $1,059.60