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 $67.53   12.838%   $76.1995   $76.20   $76.20   $76.20  
  Purchase #2 $62.38   12.248%   $70.0203   $70.02   $70.00   $70.00  
  Purchase #3 $187.89   9.331%   $205.422   $205.42   $205.40   $205.40  
  Purchase #4 $146.66   11.866%   $164.0627   $164.06   $164.05   $164.10  
  Purchase #5 $123.60   11.160%   $137.3938   $137.39   $137.40   $137.40  
  Purchase #6 $184.59   9.181%   $201.5372   $201.54   $201.55   $201.50  
  Purchase #7 $173.61   10.682%   $192.155   $192.16   $192.15   $192.20  
  7 purchase totals = $946.26       $1,046.7905   $1,046.79   $1,046.75   $1,046.80