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 $84.71   13.534%   $96.1747   $96.17   $96.15   $96.20  
  Purchase #2 $14.82   13.766%   $16.8601   $16.86   $16.85   $16.90  
  Purchase #3 $248.70   5.694%   $262.861   $262.86   $262.85   $262.90  
  Purchase #4 $86.56   10.821%   $95.9267   $95.93   $95.95   $95.90  
  Purchase #5 $219.95   11.456%   $245.1475   $245.15   $245.15   $245.10  
  Purchase #6 $220.43   8.445%   $239.0453   $239.05   $239.05   $239.00  
  Purchase #7 $100.79   8.765%   $109.6242   $109.62   $109.60   $109.60  
  7 purchase totals = $975.96       $1,065.6395   $1,065.64   $1,065.60   $1,065.60