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 $92.86   5.829%   $98.2728   $98.27   $98.25   $98.30  
  Purchase #2 $59.52   13.861%   $67.7701   $67.77   $67.75   $67.80  
  Purchase #3 $68.51   11.560%   $76.4298   $76.43   $76.45   $76.40  
  Purchase #4 $178.41   11.794%   $199.4517   $199.45   $199.45   $199.50  
  Purchase #5 $57.49   11.660%   $64.1933   $64.19   $64.20   $64.20  
  Purchase #6 $213.25   11.515%   $237.8057   $237.81   $237.80   $237.80  
  Purchase #7 $196.68   10.235%   $216.8102   $216.81   $216.80   $216.80  
  7 purchase totals = $866.72       $960.7336   $960.73   $960.70   $960.80