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 $62.42   8.259%   $67.5753   $67.58   $67.60   $67.60  
  Purchase #2 $23.36   7.833%   $25.1898   $25.19   $25.20   $25.20  
  Purchase #3 $191.92   13.266%   $217.3801   $217.38   $217.40   $217.40  
  Purchase #4 $14.54   13.297%   $16.4734   $16.47   $16.45   $16.50  
  Purchase #5 $219.74   3.348%   $227.0969   $227.10   $227.10   $227.10  
  Purchase #6 $50.27   13.124%   $56.8674   $56.87   $56.85   $56.90  
  Purchase #7 $150.47   7.517%   $161.7808   $161.78   $161.80   $161.80  
  7 purchase totals = $712.72       $772.3637   $772.37   $772.40   $772.50