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 $108.48   10.230%   $119.5775   $119.58   $119.60   $119.60  
  Purchase #2 $147.30   4.175%   $153.4498   $153.45   $153.45   $153.40  
  Purchase #3 $234.85   13.142%   $265.714   $265.71   $265.70   $265.70  
  Purchase #4 $11.64   10.848%   $12.9027   $12.90   $12.90   $12.90  
  Purchase #5 $145.39   5.184%   $152.927   $152.93   $152.95   $152.90  
  Purchase #6 $104.40   3.530%   $108.0853   $108.09   $108.10   $108.10  
  Purchase #7 $162.81   7.221%   $174.5665   $174.57   $174.55   $174.60  
  7 purchase totals = $914.87       $987.2228   $987.23   $987.25   $987.20