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 $24.37   8.138%   $26.3532   $26.35   $26.35   $26.40  
  Purchase #2 $95.90   4.122%   $99.853   $99.85   $99.85   $99.90  
  Purchase #3 $22.59   9.704%   $24.7821   $24.78   $24.80   $24.80  
  Purchase #4 $87.32   3.812%   $90.6486   $90.65   $90.65   $90.60  
  Purchase #5 $97.69   9.368%   $106.8416   $106.84   $106.85   $106.80  
  Purchase #6 $168.34   7.272%   $180.5817   $180.58   $180.60   $180.60  
  Purchase #7 $179.61   10.741%   $198.9019   $198.90   $198.90   $198.90  
  7 purchase totals = $675.82       $727.9621   $727.95   $728.00   $728.00