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 $60.87   11.696%   $67.9894   $67.99   $68.00   $68.00  
  Purchase #2 $179.97   6.853%   $192.3033   $192.30   $192.30   $192.30  
  Purchase #3 $84.45   11.779%   $94.3974   $94.40   $94.40   $94.40  
  Purchase #4 $219.89   7.799%   $237.0392   $237.04   $237.05   $237.00  
  Purchase #5 $46.49   5.606%   $49.0962   $49.10   $49.10   $49.10  
  Purchase #6 $124.96   4.633%   $130.7494   $130.75   $130.75   $130.70  
  Purchase #7 $86.86   11.112%   $96.5119   $96.51   $96.50   $96.50  
  7 purchase totals = $803.49       $868.0868   $868.09   $868.10   $868.00