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 $121.90   5.480%   $128.5801   $128.58   $128.60   $128.60  
  Purchase #2 $234.42   4.373%   $244.6712   $244.67   $244.65   $244.70  
  Purchase #3 $77.42   9.296%   $84.617   $84.62   $84.60   $84.60  
  Purchase #4 $101.76   8.804%   $110.719   $110.72   $110.70   $110.70  
  Purchase #5 $54.64   6.734%   $58.3195   $58.32   $58.30   $58.30  
  Purchase #6 $158.40   11.697%   $176.928   $176.93   $176.95   $176.90  
  Purchase #7 $233.41   10.185%   $257.1828   $257.18   $257.20   $257.20  
  7 purchase totals = $981.95       $1,061.0176   $1,061.02   $1,061.00   $1,061.00