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 $188.94   8.617%   $205.221   $205.22   $205.20   $205.20  
  Purchase #2 $69.56   10.494%   $76.8596   $76.86   $76.85   $76.90  
  Purchase #3 $149.26   7.839%   $160.9605   $160.96   $160.95   $161.00  
  Purchase #4 $217.51   9.772%   $238.7651   $238.77   $238.75   $238.80  
  Purchase #5 $14.81   5.511%   $15.6262   $15.63   $15.65   $15.60  
  Purchase #6 $59.37   7.282%   $63.6933   $63.69   $63.70   $63.70  
  Purchase #7 $213.59   8.276%   $231.2667   $231.27   $231.25   $231.30  
  7 purchase totals = $913.04       $992.3924   $992.40   $992.35   $992.50