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 $215.69   10.356%   $238.0269   $238.03   $238.05   $238.00  
  Purchase #2 $243.33   11.228%   $270.6511   $270.65   $270.65   $270.70  
  Purchase #3 $144.57   9.470%   $158.2608   $158.26   $158.25   $158.30  
  Purchase #4 $241.42   6.784%   $257.7979   $257.80   $257.80   $257.80  
  Purchase #5 $97.82   5.562%   $103.2607   $103.26   $103.25   $103.30  
  Purchase #6 $226.73   6.257%   $240.9165   $240.92   $240.90   $240.90  
  Purchase #7 $185.86   8.546%   $201.7436   $201.74   $201.75   $201.70  
  7 purchase totals = $1,355.42       $1,470.6575   $1,470.66   $1,470.65   $1,470.70