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 $73.58   3.110%   $75.8683   $75.87   $75.85   $75.90  
  Purchase #2 $248.67   9.866%   $273.2038   $273.20   $273.20   $273.20  
  Purchase #3 $73.34   12.627%   $82.6006   $82.60   $82.60   $82.60  
  Purchase #4 $149.37   9.285%   $163.239   $163.24   $163.25   $163.20  
  Purchase #5 $69.71   12.135%   $78.1693   $78.17   $78.15   $78.20  
  Purchase #6 $205.60   8.766%   $223.6229   $223.62   $223.60   $223.60  
  Purchase #7 $6.79   7.560%   $7.3033   $7.30   $7.30   $7.30  
  7 purchase totals = $827.06       $904.0072   $904.00   $903.95   $904.00