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 $21.92   9.610%   $24.0265   $24.03   $24.05   $24.00  
  Purchase #2 $131.42   3.855%   $136.4862   $136.49   $136.50   $136.50  
  Purchase #3 $50.88   7.319%   $54.6039   $54.60   $54.60   $54.60  
  Purchase #4 $170.27   3.863%   $176.8475   $176.85   $176.85   $176.80  
  Purchase #5 $59.41   4.495%   $62.0805   $62.08   $62.10   $62.10  
  Purchase #6 $226.38   5.257%   $238.2808   $238.28   $238.30   $238.30  
  Purchase #7 $67.54   3.393%   $69.8316   $69.83   $69.85   $69.80  
  7 purchase totals = $727.82       $762.1570   $762.16   $762.25   $762.10