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 $86.85   12.861%   $98.0198   $98.02   $98.00   $98.00  
  Purchase #2 $157.87   3.125%   $162.8034   $162.80   $162.80   $162.80  
  Purchase #3 $30.86   12.757%   $34.7968   $34.80   $34.80   $34.80  
  Purchase #4 $93.33   5.222%   $98.2037   $98.20   $98.20   $98.20  
  Purchase #5 $117.39   4.487%   $122.6573   $122.66   $122.65   $122.70  
  Purchase #6 $111.66   3.761%   $115.8595   $115.86   $115.85   $115.90  
  Purchase #7 $114.62   5.738%   $121.1969   $121.20   $121.20   $121.20  
  7 purchase totals = $712.58       $753.5374   $753.54   $753.50   $753.60