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 $47.80   10.188%   $52.6699   $52.67   $52.65   $52.70  
  Purchase #2 $188.79   5.765%   $199.6737   $199.67   $199.65   $199.70  
  Purchase #3 $153.62   5.814%   $162.5515   $162.55   $162.55   $162.60  
  Purchase #4 $32.91   10.243%   $36.281   $36.28   $36.30   $36.30  
  Purchase #5 $96.75   6.307%   $102.852   $102.85   $102.85   $102.90  
  Purchase #6 $102.28   11.852%   $114.4022   $114.40   $114.40   $114.40  
  Purchase #7 $172.89   11.588%   $192.9245   $192.92   $192.90   $192.90  
  7 purchase totals = $795.04       $861.3548   $861.34   $861.30   $861.50