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 $58.28   6.693%   $62.1807   $62.18   $62.20   $62.20  
  Purchase #2 $137.28   6.862%   $146.7002   $146.70   $146.70   $146.70  
  Purchase #3 $65.36   4.410%   $68.2424   $68.24   $68.25   $68.20  
  Purchase #4 $21.68   5.795%   $22.9364   $22.94   $22.95   $22.90  
  Purchase #5 $157.78   6.670%   $168.3039   $168.30   $168.30   $168.30  
  Purchase #6 $189.49   5.853%   $200.5808   $200.58   $200.60   $200.60  
  Purchase #7 $80.41   7.798%   $86.6804   $86.68   $86.70   $86.70  
  7 purchase totals = $710.28       $755.6248   $755.62   $755.70   $755.60