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 $60.73   6.220%   $64.5074   $64.51   $64.50   $64.50  
  Purchase #2 $164.34   10.543%   $181.6664   $181.67   $181.65   $181.70  
  Purchase #3 $129.61   10.690%   $143.4653   $143.47   $143.45   $143.50  
  Purchase #4 $12.30   5.130%   $12.931   $12.93   $12.95   $12.90  
  Purchase #5 $228.58   3.646%   $236.914   $236.91   $236.90   $236.90  
  Purchase #6 $67.60   12.538%   $76.0757   $76.08   $76.10   $76.10  
  Purchase #7 $96.98   10.506%   $107.1687   $107.17   $107.15   $107.20  
  7 purchase totals = $760.14       $822.7285   $822.74   $822.70   $822.80