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 $206.33   12.424%   $231.9644   $231.96   $231.95   $232.00  
  Purchase #2 $249.48   7.679%   $268.6376   $268.64   $268.65   $268.60  
  Purchase #3 $205.60   13.776%   $233.9235   $233.92   $233.90   $233.90  
  Purchase #4 $185.61   7.644%   $199.798   $199.80   $199.80   $199.80  
  Purchase #5 $239.65   8.633%   $260.339   $260.34   $260.35   $260.30  
  Purchase #6 $180.67   8.414%   $195.8716   $195.87   $195.85   $195.90  
  Purchase #7 $124.41   6.445%   $132.4282   $132.43   $132.45   $132.40  
  7 purchase totals = $1,391.75       $1,522.9623   $1,522.96   $1,522.95   $1,522.90