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 $15.77   9.410%   $17.254   $17.25   $17.25   $17.30  
  Purchase #2 $126.82   12.694%   $142.9185   $142.92   $142.90   $142.90  
  Purchase #3 $54.29   9.384%   $59.3846   $59.38   $59.40   $59.40  
  Purchase #4 $188.62   10.193%   $207.846   $207.85   $207.85   $207.80  
  Purchase #5 $239.78   6.469%   $255.2914   $255.29   $255.30   $255.30  
  Purchase #6 $43.90   5.233%   $46.1973   $46.20   $46.20   $46.20  
  Purchase #7 $114.49   4.852%   $120.0451   $120.05   $120.05   $120.00  
  7 purchase totals = $783.67       $848.9369   $848.94   $848.95   $848.90