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 $223.50   9.575%   $244.9001   $244.90   $244.90   $244.90  
  Purchase #2 $175.93   8.411%   $190.7275   $190.73   $190.75   $190.70  
  Purchase #3 $29.98   7.384%   $32.1937   $32.19   $32.20   $32.20  
  Purchase #4 $118.49   8.873%   $129.0036   $129.00   $129.00   $129.00  
  Purchase #5 $97.66   7.107%   $104.6007   $104.60   $104.60   $104.60  
  Purchase #6 $119.62   7.404%   $128.4767   $128.48   $128.50   $128.50  
  Purchase #7 $76.32   8.516%   $82.8194   $82.82   $82.80   $82.80  
  7 purchase totals = $841.50       $912.7217   $912.72   $912.75   $912.70