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 $88.49   11.274%   $98.4664   $98.47   $98.45   $98.50  
  Purchase #2 $116.87   9.269%   $127.7027   $127.70   $127.70   $127.70  
  Purchase #3 $159.86   5.849%   $169.2102   $169.21   $169.20   $169.20  
  Purchase #4 $185.72   11.472%   $207.0258   $207.03   $207.05   $207.00  
  Purchase #5 $110.75   5.277%   $116.5943   $116.59   $116.60   $116.60  
  Purchase #6 $50.41   10.743%   $55.8255   $55.83   $55.85   $55.80  
  Purchase #7 $131.87   3.222%   $136.1189   $136.12   $136.10   $136.10  
  7 purchase totals = $843.97       $910.9438   $910.95   $910.95   $910.90