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 $96.74   12.409%   $108.7445   $108.74   $108.75   $108.70  
  Purchase #2 $218.41   9.389%   $238.9165   $238.92   $238.90   $238.90  
  Purchase #3 $98.61   4.841%   $103.3837   $103.38   $103.40   $103.40  
  Purchase #4 $210.69   5.205%   $221.6564   $221.66   $221.65   $221.70  
  Purchase #5 $211.43   9.420%   $231.3467   $231.35   $231.35   $231.30  
  Purchase #6 $22.88   4.783%   $23.9744   $23.97   $23.95   $24.00  
  Purchase #7 $236.63   5.292%   $249.1525   $249.15   $249.15   $249.20  
  7 purchase totals = $1,095.39       $1,177.1747   $1,177.17   $1,177.15   $1,177.20