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 $95.62   3.149%   $98.6311   $98.63   $98.65   $98.60  
  Purchase #2 $13.79   12.840%   $15.5606   $15.56   $15.55   $15.60  
  Purchase #3 $111.43   12.649%   $125.5248   $125.52   $125.50   $125.50  
  Purchase #4 $101.68   3.365%   $105.1015   $105.10   $105.10   $105.10  
  Purchase #5 $249.80   11.658%   $278.9217   $278.92   $278.90   $278.90  
  Purchase #6 $50.58   12.772%   $57.0401   $57.04   $57.05   $57.00  
  Purchase #7 $90.64   12.652%   $102.1078   $102.11   $102.10   $102.10  
  7 purchase totals = $713.54       $782.8876   $782.88   $782.85   $782.80