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 $238.69   13.624%   $271.2091   $271.21   $271.20   $271.20  
  Purchase #2 $134.74   12.570%   $151.6768   $151.68   $151.70   $151.70  
  Purchase #3 $119.43   13.856%   $135.9782   $135.98   $136.00   $136.00  
  Purchase #4 $160.36   9.730%   $175.963   $175.96   $175.95   $176.00  
  Purchase #5 $243.36   6.792%   $259.889   $259.89   $259.90   $259.90  
  Purchase #6 $63.26   4.216%   $65.927   $65.93   $65.95   $65.90  
  Purchase #7 $165.34   4.693%   $173.0994   $173.10   $173.10   $173.10  
  7 purchase totals = $1,125.18       $1,233.7425   $1,233.75   $1,233.80   $1,233.80