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 $167.41   10.206%   $184.4959   $184.50   $184.50   $184.50  
  Purchase #2 $143.27   12.138%   $160.6601   $160.66   $160.65   $160.70  
  Purchase #3 $12.40   13.367%   $14.0575   $14.06   $14.05   $14.10  
  Purchase #4 $69.71   13.848%   $79.3634   $79.36   $79.35   $79.40  
  Purchase #5 $111.25   4.653%   $116.4265   $116.43   $116.45   $116.40  
  Purchase #6 $237.59   8.647%   $258.1344   $258.13   $258.15   $258.10  
  Purchase #7 $119.43   10.139%   $131.539   $131.54   $131.55   $131.50  
  7 purchase totals = $861.06       $944.6768   $944.68   $944.70   $944.70