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 $115.49   8.300%   $125.0757   $125.08   $125.10   $125.10  
  Purchase #2 $15.38   8.260%   $16.6504   $16.65   $16.65   $16.70  
  Purchase #3 $60.29   11.799%   $67.4036   $67.40   $67.40   $67.40  
  Purchase #4 $189.44   8.475%   $205.495   $205.50   $205.50   $205.50  
  Purchase #5 $226.45   13.245%   $256.4433   $256.44   $256.45   $256.40  
  Purchase #6 $245.70   4.684%   $257.2086   $257.21   $257.20   $257.20  
  Purchase #7 $56.65   13.782%   $64.4575   $64.46   $64.45   $64.50  
  7 purchase totals = $909.40       $992.7341   $992.74   $992.75   $992.80