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 $159.61   9.247%   $174.3691   $174.37   $174.35   $174.40  
  Purchase #2 $183.62   3.834%   $190.66   $190.66   $190.65   $190.70  
  Purchase #3 $217.74   12.497%   $244.951   $244.95   $244.95   $245.00  
  Purchase #4 $11.69   7.265%   $12.5393   $12.54   $12.55   $12.50  
  Purchase #5 $63.43   11.266%   $70.576   $70.58   $70.60   $70.60  
  Purchase #6 $103.41   10.189%   $113.9464   $113.95   $113.95   $113.90  
  Purchase #7 $173.51   8.268%   $187.8558   $187.86   $187.85   $187.90  
  7 purchase totals = $913.01       $994.8976   $994.91   $994.90   $995.00