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 $208.34   10.827%   $230.897   $230.90   $230.90   $230.90  
  Purchase #2 $64.70   12.362%   $72.6982   $72.70   $72.70   $72.70  
  Purchase #3 $48.48   9.268%   $52.9731   $52.97   $52.95   $53.00  
  Purchase #4 $8.63   13.273%   $9.7755   $9.78   $9.80   $9.80  
  Purchase #5 $102.96   10.407%   $113.675   $113.68   $113.70   $113.70  
  Purchase #6 $77.94   7.246%   $83.5875   $83.59   $83.60   $83.60  
  Purchase #7 $9.96   11.504%   $11.1058   $11.11   $11.10   $11.10  
  7 purchase totals = $521.01       $574.7121   $574.73   $574.75   $574.80