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 $53.40   6.262%   $56.7439   $56.74   $56.75   $56.70  
  Purchase #2 $129.95   11.402%   $144.7669   $144.77   $144.75   $144.80  
  Purchase #3 $155.40   13.813%   $176.8654   $176.87   $176.85   $176.90  
  Purchase #4 $24.36   5.212%   $25.6296   $25.63   $25.65   $25.60  
  Purchase #5 $116.83   7.160%   $125.195   $125.20   $125.20   $125.20  
  Purchase #6 $88.63   5.310%   $93.3363   $93.34   $93.35   $93.30  
  Purchase #7 $174.39   13.253%   $197.5019   $197.50   $197.50   $197.50  
  7 purchase totals = $742.96       $820.0390   $820.05   $820.05   $820.00