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 $188.60   13.614%   $214.276   $214.28   $214.30   $214.30  
  Purchase #2 $208.93   4.230%   $217.7677   $217.77   $217.75   $217.80  
  Purchase #3 $38.47   8.189%   $41.6203   $41.62   $41.60   $41.60  
  Purchase #4 $109.70   3.125%   $113.1281   $113.13   $113.15   $113.10  
  Purchase #5 $105.64   9.393%   $115.5628   $115.56   $115.55   $115.60  
  Purchase #6 $77.31   8.852%   $84.1535   $84.15   $84.15   $84.20  
  Purchase #7 $232.82   3.210%   $240.2935   $240.29   $240.30   $240.30  
  7 purchase totals = $961.47       $1,026.8019   $1,026.80   $1,026.80   $1,026.90