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 $82.32   12.762%   $92.8257   $92.83   $92.85   $92.80  
  Purchase #2 $69.25   6.867%   $74.0054   $74.01   $74.00   $74.00  
  Purchase #3 $120.89   9.266%   $132.0917   $132.09   $132.10   $132.10  
  Purchase #4 $224.99   7.830%   $242.6067   $242.61   $242.60   $242.60  
  Purchase #5 $15.38   13.518%   $17.4591   $17.46   $17.45   $17.50  
  Purchase #6 $217.90   3.748%   $226.0669   $226.07   $226.05   $226.10  
  Purchase #7 $29.61   9.199%   $32.3338   $32.33   $32.35   $32.30  
  7 purchase totals = $760.34       $817.3893   $817.40   $817.40   $817.40