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 $76.49   11.645%   $85.3973   $85.40   $85.40   $85.40  
  Purchase #2 $227.69   11.337%   $253.5032   $253.50   $253.50   $253.50  
  Purchase #3 $199.41   13.312%   $225.9555   $225.96   $225.95   $226.00  
  Purchase #4 $44.77   6.457%   $47.6608   $47.66   $47.65   $47.70  
  Purchase #5 $26.80   11.514%   $29.8858   $29.89   $29.90   $29.90  
  Purchase #6 $245.58   8.522%   $266.5083   $266.51   $266.50   $266.50  
  Purchase #7 $136.35   7.716%   $146.8708   $146.87   $146.85   $146.90  
  7 purchase totals = $957.09       $1,055.7817   $1,055.79   $1,055.75   $1,055.90