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 $54.65   10.702%   $60.4986   $60.50   $60.50   $60.50  
  Purchase #2 $184.35   13.181%   $208.6492   $208.65   $208.65   $208.60  
  Purchase #3 $35.44   12.286%   $39.7942   $39.79   $39.80   $39.80  
  Purchase #4 $29.99   12.856%   $33.8455   $33.85   $33.85   $33.80  
  Purchase #5 $188.25   3.385%   $194.6223   $194.62   $194.60   $194.60  
  Purchase #6 $195.67   6.128%   $207.6607   $207.66   $207.65   $207.70  
  Purchase #7 $236.59   6.733%   $252.5196   $252.52   $252.50   $252.50  
  7 purchase totals = $924.94       $997.5901   $997.59   $997.55   $997.50