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 $67.86   12.663%   $76.4531   $76.45   $76.45   $76.50  
  Purchase #2 $144.79   10.388%   $159.8308   $159.83   $159.85   $159.80  
  Purchase #3 $10.73   12.295%   $12.0493   $12.05   $12.05   $12.00  
  Purchase #4 $139.44   13.858%   $158.7636   $158.76   $158.75   $158.80  
  Purchase #5 $28.37   5.860%   $30.0325   $30.03   $30.05   $30.00  
  Purchase #6 $94.31   10.633%   $104.338   $104.34   $104.35   $104.30  
  Purchase #7 $36.36   8.620%   $39.4942   $39.49   $39.50   $39.50  
  7 purchase totals = $521.86       $580.9615   $580.95   $581.00   $580.90