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 $24.96   6.112%   $26.4856   $26.49   $26.50   $26.50  
  Purchase #2 $187.61   10.748%   $207.7743   $207.77   $207.75   $207.80  
  Purchase #3 $232.77   5.238%   $244.9625   $244.96   $244.95   $245.00  
  Purchase #4 $82.80   3.825%   $85.9671   $85.97   $85.95   $86.00  
  Purchase #5 $222.41   9.735%   $244.0616   $244.06   $244.05   $244.10  
  Purchase #6 $173.28   3.274%   $178.9532   $178.95   $178.95   $179.00  
  Purchase #7 $218.64   13.363%   $247.8569   $247.86   $247.85   $247.90  
  7 purchase totals = $1,142.47       $1,236.0612   $1,236.06   $1,236.00   $1,236.30