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 $21.25   3.840%   $22.066   $22.07   $22.05   $22.10  
  Purchase #2 $97.90   5.322%   $103.1102   $103.11   $103.10   $103.10  
  Purchase #3 $39.44   12.380%   $44.3227   $44.32   $44.30   $44.30  
  Purchase #4 $86.95   7.323%   $93.3173   $93.32   $93.30   $93.30  
  Purchase #5 $32.67   9.788%   $35.8677   $35.87   $35.85   $35.90  
  Purchase #6 $131.94   10.229%   $145.4361   $145.44   $145.45   $145.40  
  Purchase #7 $234.49   4.549%   $245.157   $245.16   $245.15   $245.20  
  7 purchase totals = $644.64       $689.2770   $689.29   $689.20   $689.30