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 $91.42   4.843%   $95.8475   $95.85   $95.85   $95.80  
  Purchase #2 $120.64   13.466%   $136.8854   $136.89   $136.90   $136.90  
  Purchase #3 $47.56   9.632%   $52.141   $52.14   $52.15   $52.10  
  Purchase #4 $58.30   6.177%   $61.9012   $61.90   $61.90   $61.90  
  Purchase #5 $244.72   13.390%   $277.488   $277.49   $277.50   $277.50  
  Purchase #6 $196.36   7.791%   $211.6584   $211.66   $211.65   $211.70  
  Purchase #7 $21.48   7.595%   $23.1114   $23.11   $23.10   $23.10  
  7 purchase totals = $780.48       $859.0329   $859.04   $859.05   $859.00