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 $33.89   8.734%   $36.85   $36.85   $36.85   $36.90  
  Purchase #2 $163.66   3.324%   $169.1001   $169.10   $169.10   $169.10  
  Purchase #3 $86.36   7.690%   $93.0011   $93.00   $93.00   $93.00  
  Purchase #4 $42.82   3.828%   $44.4591   $44.46   $44.45   $44.50  
  Purchase #5 $229.82   11.679%   $256.6607   $256.66   $256.65   $256.70  
  Purchase #6 $104.88   13.716%   $119.2653   $119.27   $119.25   $119.30  
  Purchase #7 $126.76   4.670%   $132.6797   $132.68   $132.70   $132.70  
  7 purchase totals = $788.19       $852.0160   $852.02   $852.00   $852.20