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 $61.65   7.586%   $66.3268   $66.33   $66.35   $66.30  
  Purchase #2 $178.87   5.326%   $188.3966   $188.40   $188.40   $188.40  
  Purchase #3 $139.79   3.113%   $144.1417   $144.14   $144.15   $144.10  
  Purchase #4 $239.52   11.849%   $267.9007   $267.90   $267.90   $267.90  
  Purchase #5 $172.25   11.766%   $192.5169   $192.52   $192.50   $192.50  
  Purchase #6 $126.28   4.533%   $132.0043   $132.00   $132.00   $132.00  
  Purchase #7 $218.42   5.475%   $230.3785   $230.38   $230.40   $230.40  
  7 purchase totals = $1,136.78       $1,221.6655   $1,221.67   $1,221.70   $1,221.60