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 $130.58   10.227%   $143.9344   $143.93   $143.95   $143.90  
  Purchase #2 $85.62   5.195%   $90.068   $90.07   $90.05   $90.10  
  Purchase #3 $24.88   8.447%   $26.9816   $26.98   $27.00   $27.00  
  Purchase #4 $87.66   7.779%   $94.4791   $94.48   $94.50   $94.50  
  Purchase #5 $62.82   5.412%   $66.2198   $66.22   $66.20   $66.20  
  Purchase #6 $202.76   11.621%   $226.3227   $226.32   $226.30   $226.30  
  Purchase #7 $153.88   13.309%   $174.3599   $174.36   $174.35   $174.40  
  7 purchase totals = $748.20       $822.3655   $822.36   $822.35   $822.40