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 $72.60   11.772%   $81.1465   $81.15   $81.15   $81.10  
  Purchase #2 $55.56   3.310%   $57.399   $57.40   $57.40   $57.40  
  Purchase #3 $136.91   4.274%   $142.7615   $142.76   $142.75   $142.80  
  Purchase #4 $173.37   12.119%   $194.3807   $194.38   $194.40   $194.40  
  Purchase #5 $225.95   10.528%   $249.738   $249.74   $249.75   $249.70  
  Purchase #6 $250.90   4.798%   $262.9382   $262.94   $262.95   $262.90  
  Purchase #7 $35.31   7.586%   $37.9886   $37.99   $38.00   $38.00  
  7 purchase totals = $950.60       $1,026.3525   $1,026.36   $1,026.40   $1,026.30