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 $89.38   5.116%   $93.9527   $93.95   $93.95   $94.00  
  Purchase #2 $58.85   13.586%   $66.8454   $66.85   $66.85   $66.80  
  Purchase #3 $188.27   12.796%   $212.361   $212.36   $212.35   $212.40  
  Purchase #4 $236.30   4.735%   $247.4888   $247.49   $247.50   $247.50  
  Purchase #5 $117.34   11.660%   $131.0218   $131.02   $131.00   $131.00  
  Purchase #6 $68.44   8.535%   $74.2814   $74.28   $74.30   $74.30  
  Purchase #7 $71.64   7.579%   $77.0696   $77.07   $77.05   $77.10  
  7 purchase totals = $830.22       $903.0207   $903.02   $903.00   $903.10