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 $88.72   13.811%   $100.9731   $100.97   $100.95   $101.00  
  Purchase #2 $5.27   8.225%   $5.7035   $5.70   $5.70   $5.70  
  Purchase #3 $240.26   3.176%   $247.8907   $247.89   $247.90   $247.90  
  Purchase #4 $125.62   5.453%   $132.4701   $132.47   $132.45   $132.50  
  Purchase #5 $122.91   6.308%   $130.6632   $130.66   $130.65   $130.70  
  Purchase #6 $17.34   11.263%   $19.293   $19.29   $19.30   $19.30  
  Purchase #7 $208.28   10.411%   $229.964   $229.96   $229.95   $230.00  
  7 purchase totals = $808.40       $866.9576   $866.94   $866.90   $867.10