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 $186.98   8.126%   $202.174   $202.17   $202.15   $202.20  
  Purchase #2 $222.26   6.649%   $237.0381   $237.04   $237.05   $237.00  
  Purchase #3 $113.31   5.222%   $119.227   $119.23   $119.25   $119.20  
  Purchase #4 $248.89   4.802%   $260.8417   $260.84   $260.85   $260.80  
  Purchase #5 $151.28   10.712%   $167.4851   $167.49   $167.50   $167.50  
  Purchase #6 $83.54   6.528%   $88.9935   $88.99   $89.00   $89.00  
  Purchase #7 $161.76   5.292%   $170.3203   $170.32   $170.30   $170.30  
  7 purchase totals = $1,168.02       $1,246.0797   $1,246.08   $1,246.10   $1,246.00