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 $111.92   6.525%   $119.2228   $119.22   $119.20   $119.20  
  Purchase #2 $22.58   5.175%   $23.7485   $23.75   $23.75   $23.70  
  Purchase #3 $144.62   9.142%   $157.8412   $157.84   $157.85   $157.80  
  Purchase #4 $152.85   3.649%   $158.4275   $158.43   $158.45   $158.40  
  Purchase #5 $98.59   9.604%   $108.0586   $108.06   $108.05   $108.10  
  Purchase #6 $134.74   5.622%   $142.3151   $142.32   $142.30   $142.30  
  Purchase #7 $218.64   5.453%   $230.5624   $230.56   $230.55   $230.60  
  7 purchase totals = $883.94       $940.1761   $940.18   $940.15   $940.10