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 $48.83   9.146%   $53.296   $53.30   $53.30   $53.30  
  Purchase #2 $117.42   4.563%   $122.7779   $122.78   $122.80   $122.80  
  Purchase #3 $5.27   5.562%   $5.5631   $5.56   $5.55   $5.60  
  Purchase #4 $116.63   8.517%   $126.5634   $126.56   $126.55   $126.60  
  Purchase #5 $166.69   5.425%   $175.7329   $175.73   $175.75   $175.70  
  Purchase #6 $59.55   8.194%   $64.4295   $64.43   $64.45   $64.40  
  Purchase #7 $77.93   5.632%   $82.319   $82.32   $82.30   $82.30  
  7 purchase totals = $592.32       $630.6818   $630.68   $630.70   $630.70