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 $235.67   5.805%   $249.3506   $249.35   $249.35   $249.40  
  Purchase #2 $58.58   9.681%   $64.2511   $64.25   $64.25   $64.30  
  Purchase #3 $41.62   12.397%   $46.7796   $46.78   $46.80   $46.80  
  Purchase #4 $38.40   3.266%   $39.6541   $39.65   $39.65   $39.70  
  Purchase #5 $86.60   8.661%   $94.1004   $94.10   $94.10   $94.10  
  Purchase #6 $15.49   11.471%   $17.2669   $17.27   $17.25   $17.30  
  Purchase #7 $217.87   7.830%   $234.9292   $234.93   $234.95   $234.90  
  7 purchase totals = $694.23       $746.3319   $746.33   $746.35   $746.50