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 $219.96   9.800%   $241.5161   $241.52   $241.50   $241.50  
  Purchase #2 $224.39   8.197%   $242.7832   $242.78   $242.80   $242.80  
  Purchase #3 $104.37   13.485%   $118.4443   $118.44   $118.45   $118.40  
  Purchase #4 $244.44   13.376%   $277.1363   $277.14   $277.15   $277.10  
  Purchase #5 $224.31   13.201%   $253.9212   $253.92   $253.90   $253.90  
  Purchase #6 $34.94   8.293%   $37.8376   $37.84   $37.85   $37.80  
  Purchase #7 $125.91   3.475%   $130.2854   $130.29   $130.30   $130.30  
  7 purchase totals = $1,178.32       $1,301.9241   $1,301.93   $1,301.95   $1,301.80