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 $250.31   13.568%   $284.2721   $284.27   $284.25   $284.30  
  Purchase #2 $106.96   5.324%   $112.6546   $112.65   $112.65   $112.70  
  Purchase #3 $198.78   3.637%   $206.0096   $206.01   $206.00   $206.00  
  Purchase #4 $155.44   4.558%   $162.525   $162.53   $162.55   $162.50  
  Purchase #5 $16.45   9.151%   $17.9553   $17.96   $17.95   $18.00  
  Purchase #6 $26.38   5.679%   $27.8781   $27.88   $27.90   $27.90  
  Purchase #7 $233.31   7.571%   $250.9739   $250.97   $250.95   $251.00  
  7 purchase totals = $987.63       $1,062.2686   $1,062.27   $1,062.25   $1,062.40