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 $246.69   10.527%   $272.6591   $272.66   $272.65   $272.70  
  Purchase #2 $98.92   11.499%   $110.2948   $110.29   $110.30   $110.30  
  Purchase #3 $195.74   3.466%   $202.5243   $202.52   $202.50   $202.50  
  Purchase #4 $85.27   10.248%   $94.0085   $94.01   $94.00   $94.00  
  Purchase #5 $125.81   3.249%   $129.8976   $129.90   $129.90   $129.90  
  Purchase #6 $140.44   8.171%   $151.9154   $151.92   $151.90   $151.90  
  Purchase #7 $70.25   3.382%   $72.6259   $72.63   $72.65   $72.60  
  7 purchase totals = $963.12       $1,033.9256   $1,033.93   $1,033.90   $1,033.90