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 $58.89   13.701%   $66.9585   $66.96   $66.95   $67.00  
  Purchase #2 $217.95   8.664%   $236.8332   $236.83   $236.85   $236.80  
  Purchase #3 $176.27   13.411%   $199.9096   $199.91   $199.90   $199.90  
  Purchase #4 $250.52   11.227%   $278.6459   $278.65   $278.65   $278.60  
  Purchase #5 $22.59   7.388%   $24.2589   $24.26   $24.25   $24.30  
  Purchase #6 $68.32   6.811%   $72.9733   $72.97   $72.95   $73.00  
  Purchase #7 $216.34   9.324%   $236.5115   $236.51   $236.50   $236.50  
  7 purchase totals = $1,010.88       $1,116.0909   $1,116.09   $1,116.05   $1,116.10