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 $247.35   7.535%   $265.9878   $265.99   $266.00   $266.00  
  Purchase #2 $85.65   12.466%   $96.3271   $96.33   $96.35   $96.30  
  Purchase #3 $223.42   8.663%   $242.7749   $242.77   $242.75   $242.80  
  Purchase #4 $124.28   6.131%   $131.8996   $131.90   $131.90   $131.90  
  Purchase #5 $199.92   8.794%   $217.501   $217.50   $217.50   $217.50  
  Purchase #6 $170.38   13.541%   $193.4512   $193.45   $193.45   $193.50  
  Purchase #7 $188.33   7.725%   $202.8785   $202.88   $202.90   $202.90  
  7 purchase totals = $1,239.33       $1,350.8201   $1,350.82   $1,350.85   $1,350.90