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 $126.47   13.839%   $143.9722   $143.97   $143.95   $144.00  
  Purchase #2 $167.60   10.283%   $184.8343   $184.83   $184.85   $184.80  
  Purchase #3 $73.25   12.538%   $82.4341   $82.43   $82.45   $82.40  
  Purchase #4 $227.84   6.555%   $242.7749   $242.77   $242.75   $242.80  
  Purchase #5 $221.79   13.625%   $252.0089   $252.01   $252.00   $252.00  
  Purchase #6 $188.51   13.306%   $213.5931   $213.59   $213.60   $213.60  
  Purchase #7 $119.92   4.410%   $125.2085   $125.21   $125.20   $125.20  
  7 purchase totals = $1,125.38       $1,244.8260   $1,244.81   $1,244.80   $1,244.80