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 $97.93   11.813%   $109.4985   $109.50   $109.50   $109.50  
  Purchase #2 $44.51   8.520%   $48.3023   $48.30   $48.30   $48.30  
  Purchase #3 $60.61   7.275%   $65.0194   $65.02   $65.00   $65.00  
  Purchase #4 $234.36   5.718%   $247.7607   $247.76   $247.75   $247.80  
  Purchase #5 $176.62   8.303%   $191.2848   $191.28   $191.30   $191.30  
  Purchase #6 $241.92   13.549%   $274.6977   $274.70   $274.70   $274.70  
  Purchase #7 $74.97   6.348%   $79.7291   $79.73   $79.75   $79.70  
  7 purchase totals = $930.92       $1,016.2925   $1,016.29   $1,016.30   $1,016.30