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 $198.67   13.803%   $226.0924   $226.09   $226.10   $226.10  
  Purchase #2 $43.69   7.129%   $46.8047   $46.80   $46.80   $46.80  
  Purchase #3 $119.38   4.349%   $124.5718   $124.57   $124.55   $124.60  
  Purchase #4 $158.29   9.723%   $173.6805   $173.68   $173.70   $173.70  
  Purchase #5 $63.57   12.368%   $71.4323   $71.43   $71.45   $71.40  
  Purchase #6 $226.97   8.126%   $245.4136   $245.41   $245.40   $245.40  
  Purchase #7 $51.35   5.637%   $54.2446   $54.24   $54.25   $54.20  
  7 purchase totals = $861.92       $942.2399   $942.22   $942.25   $942.20