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 $86.92   12.737%   $97.991   $97.99   $98.00   $98.00  
  Purchase #2 $227.46   6.248%   $241.6717   $241.67   $241.65   $241.70  
  Purchase #3 $71.89   3.636%   $74.5039   $74.50   $74.50   $74.50  
  Purchase #4 $26.88   11.286%   $29.9137   $29.91   $29.90   $29.90  
  Purchase #5 $231.87   11.159%   $257.7444   $257.74   $257.75   $257.70  
  Purchase #6 $227.72   10.723%   $252.1384   $252.14   $252.15   $252.10  
  Purchase #7 $192.45   9.276%   $210.3017   $210.30   $210.30   $210.30  
  7 purchase totals = $1,065.19       $1,164.2648   $1,164.25   $1,164.25   $1,164.20