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 $248.67   7.239%   $266.6712   $266.67   $266.65   $266.70  
  Purchase #2 $114.44   5.217%   $120.4103   $120.41   $120.40   $120.40  
  Purchase #3 $42.42   5.785%   $44.874   $44.87   $44.85   $44.90  
  Purchase #4 $117.67   13.726%   $133.8214   $133.82   $133.80   $133.80  
  Purchase #5 $127.70   11.271%   $142.0931   $142.09   $142.10   $142.10  
  Purchase #6 $141.46   7.445%   $151.9917   $151.99   $152.00   $152.00  
  Purchase #7 $195.62   4.610%   $204.6381   $204.64   $204.65   $204.60  
  7 purchase totals = $987.98       $1,064.4998   $1,064.49   $1,064.45   $1,064.50