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 $116.58   3.445%   $120.5962   $120.60   $120.60   $120.60  
  Purchase #2 $85.47   8.511%   $92.7444   $92.74   $92.75   $92.70  
  Purchase #3 $106.39   12.581%   $119.7749   $119.77   $119.75   $119.80  
  Purchase #4 $250.39   4.623%   $261.9655   $261.97   $261.95   $262.00  
  Purchase #5 $27.41   6.165%   $29.0998   $29.10   $29.10   $29.10  
  Purchase #6 $75.49   8.762%   $82.1044   $82.10   $82.10   $82.10  
  Purchase #7 $36.54   9.697%   $40.0833   $40.08   $40.10   $40.10  
  7 purchase totals = $698.27       $746.3685   $746.36   $746.35   $746.40