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 $183.91   11.262%   $204.6219   $204.62   $204.60   $204.60  
  Purchase #2 $150.61   11.849%   $168.4558   $168.46   $168.45   $168.50  
  Purchase #3 $244.45   11.338%   $272.1657   $272.17   $272.15   $272.20  
  Purchase #4 $247.29   5.252%   $260.2777   $260.28   $260.30   $260.30  
  Purchase #5 $209.83   7.457%   $225.477   $225.48   $225.50   $225.50  
  Purchase #6 $126.78   9.482%   $138.8013   $138.80   $138.80   $138.80  
  Purchase #7 $237.81   11.763%   $265.7836   $265.78   $265.80   $265.80  
  7 purchase totals = $1,400.68       $1,535.5830   $1,535.59   $1,535.60   $1,535.70