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 $233.99   12.243%   $262.6374   $262.64   $262.65   $262.60  
  Purchase #2 $158.74   10.292%   $175.0775   $175.08   $175.10   $175.10  
  Purchase #3 $11.50   11.409%   $12.812   $12.81   $12.80   $12.80  
  Purchase #4 $65.63   10.600%   $72.5868   $72.59   $72.60   $72.60  
  Purchase #5 $23.84   5.410%   $25.1297   $25.13   $25.15   $25.10  
  Purchase #6 $199.44   12.696%   $224.7609   $224.76   $224.75   $224.80  
  Purchase #7 $59.60   4.610%   $62.3476   $62.35   $62.35   $62.30  
  7 purchase totals = $752.74       $835.3519   $835.36   $835.40   $835.30