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 $124.54   5.380%   $131.2403   $131.24   $131.25   $131.20  
  Purchase #2 $141.69   4.727%   $148.3877   $148.39   $148.40   $148.40  
  Purchase #3 $41.59   10.666%   $46.026   $46.03   $46.05   $46.00  
  Purchase #4 $70.34   8.308%   $76.1838   $76.18   $76.20   $76.20  
  Purchase #5 $127.74   5.582%   $134.8704   $134.87   $134.85   $134.90  
  Purchase #6 $90.47   8.135%   $97.8297   $97.83   $97.85   $97.80  
  Purchase #7 $134.28   12.851%   $151.5363   $151.54   $151.55   $151.50  
  7 purchase totals = $730.65       $786.0742   $786.08   $786.15   $786.00