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 $53.47   11.825%   $59.7928   $59.79   $59.80   $59.80  
  Purchase #2 $141.30   9.163%   $154.2473   $154.25   $154.25   $154.20  
  Purchase #3 $89.79   7.725%   $96.7263   $96.73   $96.75   $96.70  
  Purchase #4 $244.29   3.527%   $252.9061   $252.91   $252.90   $252.90  
  Purchase #5 $29.58   11.610%   $33.0142   $33.01   $33.00   $33.00  
  Purchase #6 $182.33   7.145%   $195.3575   $195.36   $195.35   $195.40  
  Purchase #7 $184.42   9.258%   $201.4936   $201.49   $201.50   $201.50  
  7 purchase totals = $925.18       $993.5378   $993.54   $993.55   $993.50