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 $57.69   8.386%   $62.5279   $62.53   $62.55   $62.50  
  Purchase #2 $7.57   13.437%   $8.5872   $8.59   $8.60   $8.60  
  Purchase #3 $104.39   11.770%   $116.6767   $116.68   $116.70   $116.70  
  Purchase #4 $131.67   6.534%   $140.2733   $140.27   $140.25   $140.30  
  Purchase #5 $141.55   9.489%   $154.9817   $154.98   $155.00   $155.00  
  Purchase #6 $112.58   5.548%   $118.8259   $118.83   $118.85   $118.80  
  Purchase #7 $135.81   11.621%   $151.5925   $151.59   $151.60   $151.60  
  7 purchase totals = $691.26       $753.4652   $753.47   $753.55   $753.50