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 $117.84   11.178%   $131.0122   $131.01   $131.00   $131.00  
  Purchase #2 $240.54   8.122%   $260.0767   $260.08   $260.10   $260.10  
  Purchase #3 $234.34   9.742%   $257.1694   $257.17   $257.15   $257.20  
  Purchase #4 $112.62   7.748%   $121.3458   $121.35   $121.35   $121.30  
  Purchase #5 $164.61   5.625%   $173.8693   $173.87   $173.85   $173.90  
  Purchase #6 $237.40   6.154%   $252.0096   $252.01   $252.00   $252.00  
  Purchase #7 $239.81   6.110%   $254.4624   $254.46   $254.45   $254.50  
  7 purchase totals = $1,347.16       $1,449.9454   $1,449.95   $1,449.90   $1,450.00