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 $170.57   8.613%   $185.2612   $185.26   $185.25   $185.30  
  Purchase #2 $125.64   6.660%   $134.0076   $134.01   $134.00   $134.00  
  Purchase #3 $215.63   6.266%   $229.1414   $229.14   $229.15   $229.10  
  Purchase #4 $95.29   6.316%   $101.3085   $101.31   $101.30   $101.30  
  Purchase #5 $235.28   9.529%   $257.6998   $257.70   $257.70   $257.70  
  Purchase #6 $154.44   4.227%   $160.9682   $160.97   $160.95   $161.00  
  Purchase #7 $139.29   8.345%   $150.9138   $150.91   $150.90   $150.90  
  7 purchase totals = $1,136.14       $1,219.3005   $1,219.30   $1,219.25   $1,219.30