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 $22.35   11.442%   $24.9073   $24.91   $24.90   $24.90  
  Purchase #2 $216.81   4.834%   $227.2906   $227.29   $227.30   $227.30  
  Purchase #3 $48.49   8.742%   $52.729   $52.73   $52.75   $52.70  
  Purchase #4 $60.62   11.130%   $67.367   $67.37   $67.35   $67.40  
  Purchase #5 $77.91   13.306%   $88.2767   $88.28   $88.30   $88.30  
  Purchase #6 $95.89   4.866%   $100.556   $100.56   $100.55   $100.60  
  Purchase #7 $220.54   11.577%   $246.0719   $246.07   $246.05   $246.10  
  7 purchase totals = $742.61       $807.1985   $807.21   $807.20   $807.30