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 $71.75   9.587%   $78.6287   $78.63   $78.65   $78.60  
  Purchase #2 $223.92   7.615%   $240.9715   $240.97   $240.95   $241.00  
  Purchase #3 $24.75   11.117%   $27.5015   $27.50   $27.50   $27.50  
  Purchase #4 $119.73   4.672%   $125.3238   $125.32   $125.30   $125.30  
  Purchase #5 $43.60   5.546%   $46.0181   $46.02   $46.00   $46.00  
  Purchase #6 $202.66   9.242%   $221.3898   $221.39   $221.40   $221.40  
  Purchase #7 $19.60   6.328%   $20.8403   $20.84   $20.85   $20.80  
  7 purchase totals = $706.01       $760.6737   $760.67   $760.65   $760.60