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 $82.63   10.467%   $91.2789   $91.28   $91.30   $91.30  
  Purchase #2 $141.92   6.395%   $150.9958   $151.00   $151.00   $151.00  
  Purchase #3 $185.34   3.784%   $192.3533   $192.35   $192.35   $192.40  
  Purchase #4 $85.44   9.383%   $93.4568   $93.46   $93.45   $93.50  
  Purchase #5 $55.87   8.332%   $60.5251   $60.53   $60.55   $60.50  
  Purchase #6 $109.90   5.735%   $116.2028   $116.20   $116.20   $116.20  
  Purchase #7 $102.27   12.428%   $114.9801   $114.98   $115.00   $115.00  
  7 purchase totals = $763.37       $819.7928   $819.80   $819.85   $819.90