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 $139.40   8.144%   $150.7527   $150.75   $150.75   $150.80  
  Purchase #2 $158.41   11.282%   $176.2818   $176.28   $176.30   $176.30  
  Purchase #3 $108.41   3.556%   $112.2651   $112.27   $112.25   $112.30  
  Purchase #4 $239.87   11.248%   $266.8506   $266.85   $266.85   $266.90  
  Purchase #5 $20.74   9.124%   $22.6323   $22.63   $22.65   $22.60  
  Purchase #6 $64.34   3.385%   $66.5179   $66.52   $66.50   $66.50  
  Purchase #7 $214.57   5.866%   $227.1567   $227.16   $227.15   $227.20  
  7 purchase totals = $945.74       $1,022.4571   $1,022.46   $1,022.45   $1,022.60