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 $86.25   13.159%   $97.5996   $97.60   $97.60   $97.60  
  Purchase #2 $162.89   4.735%   $170.6028   $170.60   $170.60   $170.60  
  Purchase #3 $106.73   4.851%   $111.9075   $111.91   $111.90   $111.90  
  Purchase #4 $241.48   10.516%   $266.874   $266.87   $266.85   $266.90  
  Purchase #5 $23.61   11.508%   $26.327   $26.33   $26.35   $26.30  
  Purchase #6 $76.94   13.111%   $87.0276   $87.03   $87.05   $87.00  
  Purchase #7 $141.75   10.857%   $157.1398   $157.14   $157.15   $157.10  
  7 purchase totals = $839.65       $917.4783   $917.48   $917.50   $917.40