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 $249.49   6.829%   $266.5277   $266.53   $266.55   $266.50  
  Purchase #2 $74.47   10.347%   $82.1754   $82.18   $82.20   $82.20  
  Purchase #3 $9.66   10.205%   $10.6458   $10.65   $10.65   $10.60  
  Purchase #4 $177.40   13.632%   $201.5832   $201.58   $201.60   $201.60  
  Purchase #5 $176.82   9.660%   $193.9008   $193.90   $193.90   $193.90  
  Purchase #6 $117.59   4.235%   $122.5699   $122.57   $122.55   $122.60  
  Purchase #7 $165.64   3.814%   $171.9575   $171.96   $171.95   $172.00  
  7 purchase totals = $971.07       $1,049.3603   $1,049.37   $1,049.40   $1,049.40