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 $22.65   8.302%   $24.5304   $24.53   $24.55   $24.50  
  Purchase #2 $236.34   6.549%   $251.8179   $251.82   $251.80   $251.80  
  Purchase #3 $87.64   10.166%   $96.5495   $96.55   $96.55   $96.50  
  Purchase #4 $72.85   6.587%   $77.6486   $77.65   $77.65   $77.60  
  Purchase #5 $24.77   8.108%   $26.7784   $26.78   $26.80   $26.80  
  Purchase #6 $206.43   8.786%   $224.5669   $224.57   $224.55   $224.60  
  Purchase #7 $182.26   12.193%   $204.483   $204.48   $204.50   $204.50  
  7 purchase totals = $832.94       $906.3747   $906.38   $906.40   $906.30