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 $91.46   5.662%   $96.6385   $96.64   $96.65   $96.60  
  Purchase #2 $202.46   4.872%   $212.3239   $212.32   $212.30   $212.30  
  Purchase #3 $51.50   8.434%   $55.8435   $55.84   $55.85   $55.80  
  Purchase #4 $140.89   9.385%   $154.1125   $154.11   $154.10   $154.10  
  Purchase #5 $125.36   9.731%   $137.5588   $137.56   $137.55   $137.60  
  Purchase #6 $15.38   12.716%   $17.3357   $17.34   $17.35   $17.30  
  Purchase #7 $167.35   12.600%   $188.4361   $188.44   $188.45   $188.40  
  7 purchase totals = $794.40       $862.2490   $862.25   $862.25   $862.10