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 $226.37   10.766%   $250.741   $250.74   $250.75   $250.70  
  Purchase #2 $49.39   8.343%   $53.5106   $53.51   $53.50   $53.50  
  Purchase #3 $169.33   9.259%   $185.0083   $185.01   $185.00   $185.00  
  Purchase #4 $192.49   11.665%   $214.944   $214.94   $214.95   $214.90  
  Purchase #5 $8.37   11.840%   $9.361   $9.36   $9.35   $9.40  
  Purchase #6 $244.95   12.251%   $274.9588   $274.96   $274.95   $275.00  
  Purchase #7 $121.67   11.793%   $136.0185   $136.02   $136.00   $136.00  
  7 purchase totals = $1,012.57       $1,124.5422   $1,124.54   $1,124.50   $1,124.50