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 $44.93   5.825%   $47.5472   $47.55   $47.55   $47.50  
  Purchase #2 $37.92   13.298%   $42.9626   $42.96   $42.95   $43.00  
  Purchase #3 $205.70   9.837%   $225.9347   $225.93   $225.95   $225.90  
  Purchase #4 $93.67   8.361%   $101.5017   $101.50   $101.50   $101.50  
  Purchase #5 $195.91   5.671%   $207.0201   $207.02   $207.00   $207.00  
  Purchase #6 $166.93   4.559%   $174.5403   $174.54   $174.55   $174.50  
  Purchase #7 $148.40   10.360%   $163.7742   $163.77   $163.75   $163.80  
  7 purchase totals = $893.46       $963.2808   $963.27   $963.25   $963.20