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 $87.61   12.544%   $98.5998   $98.60   $98.60   $98.60  
  Purchase #2 $226.54   13.770%   $257.7346   $257.73   $257.75   $257.70  
  Purchase #3 $237.69   6.709%   $253.6366   $253.64   $253.65   $253.60  
  Purchase #4 $172.94   5.832%   $183.0259   $183.03   $183.05   $183.00  
  Purchase #5 $158.85   5.127%   $166.9942   $166.99   $167.00   $167.00  
  Purchase #6 $231.38   3.758%   $240.0753   $240.08   $240.10   $240.10  
  Purchase #7 $63.87   3.355%   $66.0128   $66.01   $66.00   $66.00  
  7 purchase totals = $1,178.88       $1,266.0792   $1,266.08   $1,266.15   $1,266.00