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 $188.95   6.523%   $201.2752   $201.28   $201.30   $201.30  
  Purchase #2 $89.50   6.423%   $95.2486   $95.25   $95.25   $95.20  
  Purchase #3 $44.33   12.262%   $49.7657   $49.77   $49.75   $49.80  
  Purchase #4 $155.51   7.707%   $167.4952   $167.50   $167.50   $167.50  
  Purchase #5 $114.62   12.151%   $128.5475   $128.55   $128.55   $128.50  
  Purchase #6 $246.83   7.831%   $266.1593   $266.16   $266.15   $266.20  
  Purchase #7 $125.41   5.275%   $132.0254   $132.03   $132.05   $132.00  
  7 purchase totals = $965.15       $1,040.5169   $1,040.54   $1,040.55   $1,040.50