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 $169.69   8.553%   $184.2036   $184.20   $184.20   $184.20  
  Purchase #2 $54.57   5.523%   $57.5839   $57.58   $57.60   $57.60  
  Purchase #3 $103.30   10.322%   $113.9626   $113.96   $113.95   $114.00  
  Purchase #4 $133.56   13.825%   $152.0247   $152.02   $152.00   $152.00  
  Purchase #5 $175.80   9.536%   $192.5643   $192.56   $192.55   $192.60  
  Purchase #6 $7.73   6.156%   $8.2059   $8.21   $8.20   $8.20  
  Purchase #7 $51.48   11.606%   $57.4548   $57.45   $57.45   $57.50  
  7 purchase totals = $696.13       $765.9998   $765.98   $765.95   $766.10