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 $84.64   8.369%   $91.7235   $91.72   $91.70   $91.70  
  Purchase #2 $57.68   13.736%   $65.6029   $65.60   $65.60   $65.60  
  Purchase #3 $157.77   6.746%   $168.4132   $168.41   $168.40   $168.40  
  Purchase #4 $48.30   13.339%   $54.7427   $54.74   $54.75   $54.70  
  Purchase #5 $200.29   7.148%   $214.6067   $214.61   $214.60   $214.60  
  Purchase #6 $93.98   3.439%   $97.212   $97.21   $97.20   $97.20  
  Purchase #7 $12.41   8.338%   $13.4447   $13.44   $13.45   $13.40  
  7 purchase totals = $655.07       $705.7457   $705.73   $705.70   $705.60