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 $88.71   7.233%   $95.1264   $95.13   $95.15   $95.10  
  Purchase #2 $35.44   13.108%   $40.0855   $40.09   $40.10   $40.10  
  Purchase #3 $45.54   13.197%   $51.5499   $51.55   $51.55   $51.50  
  Purchase #4 $91.30   5.533%   $96.3516   $96.35   $96.35   $96.40  
  Purchase #5 $211.93   4.389%   $221.2316   $221.23   $221.25   $221.20  
  Purchase #6 $247.49   9.842%   $271.848   $271.85   $271.85   $271.80  
  Purchase #7 $77.80   8.429%   $84.3578   $84.36   $84.35   $84.40  
  7 purchase totals = $798.21       $860.5508   $860.56   $860.60   $860.50