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 $147.37   13.307%   $166.9805   $166.98   $167.00   $167.00  
  Purchase #2 $153.69   13.126%   $173.8633   $173.86   $173.85   $173.90  
  Purchase #3 $104.55   7.376%   $112.2616   $112.26   $112.25   $112.30  
  Purchase #4 $194.49   7.597%   $209.2654   $209.27   $209.25   $209.30  
  Purchase #5 $94.86   9.796%   $104.1525   $104.15   $104.15   $104.20  
  Purchase #6 $213.93   10.455%   $236.2964   $236.30   $236.30   $236.30  
  Purchase #7 $242.46   12.360%   $272.4281   $272.43   $272.45   $272.40  
  7 purchase totals = $1,151.35       $1,275.2478   $1,275.25   $1,275.25   $1,275.40