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 $77.94   10.617%   $86.2149   $86.21   $86.20   $86.20  
  Purchase #2 $91.94   11.243%   $102.2768   $102.28   $102.30   $102.30  
  Purchase #3 $177.55   9.865%   $195.0653   $195.07   $195.05   $195.10  
  Purchase #4 $220.67   9.377%   $241.3622   $241.36   $241.35   $241.40  
  Purchase #5 $66.70   11.859%   $74.61   $74.61   $74.60   $74.60  
  Purchase #6 $90.39   4.663%   $94.6049   $94.60   $94.60   $94.60  
  Purchase #7 $76.93   8.557%   $83.5129   $83.51   $83.50   $83.50  
  7 purchase totals = $802.12       $877.6470   $877.64   $877.60   $877.70