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 $91.86   5.865%   $97.2476   $97.25   $97.25   $97.20  
  Purchase #2 $49.39   4.286%   $51.5069   $51.51   $51.50   $51.50  
  Purchase #3 $105.77   7.565%   $113.7715   $113.77   $113.75   $113.80  
  Purchase #4 $238.88   9.573%   $261.748   $261.75   $261.75   $261.70  
  Purchase #5 $59.25   10.644%   $65.5566   $65.56   $65.55   $65.60  
  Purchase #6 $235.95   6.246%   $250.6874   $250.69   $250.70   $250.70  
  Purchase #7 $40.65   8.276%   $44.0142   $44.01   $44.00   $44.00  
  7 purchase totals = $821.75       $884.5322   $884.54   $884.50   $884.50