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 $214.54   11.412%   $239.0233   $239.02   $239.00   $239.00  
  Purchase #2 $101.62   11.364%   $113.1681   $113.17   $113.15   $113.20  
  Purchase #3 $12.34   7.187%   $13.2269   $13.23   $13.25   $13.20  
  Purchase #4 $23.49   10.768%   $26.0194   $26.02   $26.00   $26.00  
  Purchase #5 $84.47   13.412%   $95.7991   $95.80   $95.80   $95.80  
  Purchase #6 $103.84   6.234%   $110.3134   $110.31   $110.30   $110.30  
  Purchase #7 $209.90   9.117%   $229.0366   $229.04   $229.05   $229.00  
  7 purchase totals = $750.20       $826.5868   $826.59   $826.55   $826.50