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 $184.75   12.456%   $207.7625   $207.76   $207.75   $207.80  
  Purchase #2 $66.76   12.806%   $75.3093   $75.31   $75.30   $75.30  
  Purchase #3 $116.46   6.187%   $123.6654   $123.67   $123.65   $123.70  
  Purchase #4 $113.62   3.532%   $117.6331   $117.63   $117.65   $117.60  
  Purchase #5 $188.95   5.826%   $199.9582   $199.96   $199.95   $200.00  
  Purchase #6 $71.82   3.447%   $74.2956   $74.30   $74.30   $74.30  
  Purchase #7 $156.48   4.624%   $163.7156   $163.72   $163.70   $163.70  
  7 purchase totals = $898.84       $962.3397   $962.35   $962.30   $962.40