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 $97.69   9.432%   $106.9041   $106.90   $106.90   $106.90  
  Purchase #2 $13.48   4.841%   $14.1326   $14.13   $14.15   $14.10  
  Purchase #3 $112.69   11.747%   $125.9277   $125.93   $125.95   $125.90  
  Purchase #4 $239.95   3.578%   $248.5354   $248.54   $248.55   $248.50  
  Purchase #5 $37.85   9.341%   $41.3856   $41.39   $41.40   $41.40  
  Purchase #6 $95.42   6.627%   $101.7435   $101.74   $101.75   $101.70  
  Purchase #7 $65.68   6.484%   $69.9387   $69.94   $69.95   $69.90  
  7 purchase totals = $662.76       $708.5676   $708.57   $708.65   $708.40