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 $219.95   4.182%   $229.1483   $229.15   $229.15   $229.10  
  Purchase #2 $72.90   12.172%   $81.7734   $81.77   $81.75   $81.80  
  Purchase #3 $86.79   8.166%   $93.8773   $93.88   $93.90   $93.90  
  Purchase #4 $61.95   10.237%   $68.2918   $68.29   $68.30   $68.30  
  Purchase #5 $203.63   5.448%   $214.7238   $214.72   $214.70   $214.70  
  Purchase #6 $236.37   13.237%   $267.6583   $267.66   $267.65   $267.70  
  Purchase #7 $62.40   6.576%   $66.5034   $66.50   $66.50   $66.50  
  7 purchase totals = $943.99       $1,021.9763   $1,021.97   $1,021.95   $1,022.00