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 $44.92   8.228%   $48.616   $48.62   $48.60   $48.60  
  Purchase #2 $187.30   13.440%   $212.4731   $212.47   $212.45   $212.50  
  Purchase #3 $83.35   12.754%   $93.9805   $93.98   $94.00   $94.00  
  Purchase #4 $243.46   4.232%   $253.7632   $253.76   $253.75   $253.80  
  Purchase #5 $76.87   3.735%   $79.7411   $79.74   $79.75   $79.70  
  Purchase #6 $147.30   11.167%   $163.749   $163.75   $163.75   $163.70  
  Purchase #7 $7.69   10.508%   $8.4981   $8.50   $8.50   $8.50  
  7 purchase totals = $790.89       $860.8210   $860.82   $860.80   $860.80