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 $245.37   8.621%   $266.5233   $266.52   $266.50   $266.50  
  Purchase #2 $88.27   6.513%   $94.019   $94.02   $94.00   $94.00  
  Purchase #3 $235.48   4.635%   $246.3945   $246.39   $246.40   $246.40  
  Purchase #4 $180.56   4.569%   $188.8098   $188.81   $188.80   $188.80  
  Purchase #5 $159.31   10.869%   $176.6254   $176.63   $176.65   $176.60  
  Purchase #6 $16.92   13.141%   $19.1435   $19.14   $19.15   $19.10  
  Purchase #7 $191.46   8.314%   $207.378   $207.38   $207.40   $207.40  
  7 purchase totals = $1,117.37       $1,198.8935   $1,198.89   $1,198.90   $1,198.80