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 $249.95   10.670%   $276.6197   $276.62   $276.60   $276.60  
  Purchase #2 $79.98   8.229%   $86.5616   $86.56   $86.55   $86.60  
  Purchase #3 $31.59   9.535%   $34.6021   $34.60   $34.60   $34.60  
  Purchase #4 $129.42   13.431%   $146.8024   $146.80   $146.80   $146.80  
  Purchase #5 $234.59   8.561%   $254.6732   $254.67   $254.65   $254.70  
  Purchase #6 $227.36   9.874%   $249.8095   $249.81   $249.80   $249.80  
  Purchase #7 $51.42   7.805%   $55.4333   $55.43   $55.45   $55.40  
  7 purchase totals = $1,004.31       $1,104.5018   $1,104.49   $1,104.45   $1,104.50