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 $113.91   9.578%   $124.8203   $124.82   $124.80   $124.80  
  Purchase #2 $58.88   4.795%   $61.7033   $61.70   $61.70   $61.70  
  Purchase #3 $119.98   9.630%   $131.5341   $131.53   $131.55   $131.50  
  Purchase #4 $54.56   8.505%   $59.2003   $59.20   $59.20   $59.20  
  Purchase #5 $191.80   5.649%   $202.6348   $202.63   $202.65   $202.60  
  Purchase #6 $140.63   13.606%   $159.7641   $159.76   $159.75   $159.80  
  Purchase #7 $223.27   11.250%   $248.3879   $248.39   $248.40   $248.40  
  7 purchase totals = $903.03       $988.0448   $988.03   $988.05   $988.00