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 $32.44   10.469%   $35.8361   $35.84   $35.85   $35.80  
  Purchase #2 $152.53   6.124%   $161.8709   $161.87   $161.85   $161.90  
  Purchase #3 $135.80   3.634%   $140.735   $140.74   $140.75   $140.70  
  Purchase #4 $66.73   7.369%   $71.6473   $71.65   $71.65   $71.60  
  Purchase #5 $129.84   12.763%   $146.4115   $146.41   $146.40   $146.40  
  Purchase #6 $234.64   7.318%   $251.811   $251.81   $251.80   $251.80  
  Purchase #7 $210.55   5.207%   $221.5133   $221.51   $221.50   $221.50  
  7 purchase totals = $962.53       $1,029.8251   $1,029.83   $1,029.80   $1,029.70