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 $98.55   12.489%   $110.8579   $110.86   $110.85   $110.90  
  Purchase #2 $245.63   13.350%   $278.4216   $278.42   $278.40   $278.40  
  Purchase #3 $121.91   10.804%   $135.0812   $135.08   $135.10   $135.10  
  Purchase #4 $37.92   5.359%   $39.9521   $39.95   $39.95   $40.00  
  Purchase #5 $114.55   8.202%   $123.9454   $123.95   $123.95   $123.90  
  Purchase #6 $69.73   5.511%   $73.5728   $73.57   $73.55   $73.60  
  Purchase #7 $74.73   10.544%   $82.6095   $82.61   $82.60   $82.60  
  7 purchase totals = $763.02       $844.4405   $844.44   $844.40   $844.50