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 $205.27   8.143%   $221.9851   $221.99   $222.00   $222.00  
  Purchase #2 $81.41   8.644%   $88.4471   $88.45   $88.45   $88.40  
  Purchase #3 $124.64   9.484%   $136.4609   $136.46   $136.45   $136.50  
  Purchase #4 $238.28   10.225%   $262.6441   $262.64   $262.65   $262.60  
  Purchase #5 $31.34   8.341%   $33.9541   $33.95   $33.95   $34.00  
  Purchase #6 $71.41   5.725%   $75.4982   $75.50   $75.50   $75.50  
  Purchase #7 $123.89   9.782%   $136.0089   $136.01   $136.00   $136.00  
  7 purchase totals = $876.24       $954.9984   $955.00   $955.00   $955.00