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 $54.73   6.347%   $58.2037   $58.20   $58.20   $58.20  
  Purchase #2 $220.89   11.349%   $245.9588   $245.96   $245.95   $246.00  
  Purchase #3 $246.50   5.531%   $260.1339   $260.13   $260.15   $260.10  
  Purchase #4 $223.54   9.707%   $245.239   $245.24   $245.25   $245.20  
  Purchase #5 $223.34   5.758%   $236.1999   $236.20   $236.20   $236.20  
  Purchase #6 $119.90   8.715%   $130.3493   $130.35   $130.35   $130.30  
  Purchase #7 $59.90   7.268%   $64.2535   $64.25   $64.25   $64.30  
  7 purchase totals = $1,148.80       $1,240.3381   $1,240.33   $1,240.35   $1,240.30