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 $7.95   8.157%   $8.5985   $8.60   $8.60   $8.60  
  Purchase #2 $237.49   12.717%   $267.6916   $267.69   $267.70   $267.70  
  Purchase #3 $44.44   4.561%   $46.4669   $46.47   $46.45   $46.50  
  Purchase #4 $171.90   6.338%   $182.795   $182.80   $182.80   $182.80  
  Purchase #5 $220.61   8.296%   $238.9118   $238.91   $238.90   $238.90  
  Purchase #6 $179.59   9.511%   $196.6708   $196.67   $196.65   $196.70  
  Purchase #7 $67.89   4.476%   $70.9288   $70.93   $70.95   $70.90  
  7 purchase totals = $929.87       $1,012.0634   $1,012.07   $1,012.05   $1,012.10