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 $202.85   6.807%   $216.658   $216.66   $216.65   $216.70  
  Purchase #2 $106.35   5.230%   $111.9121   $111.91   $111.90   $111.90  
  Purchase #3 $132.76   7.149%   $142.251   $142.25   $142.25   $142.30  
  Purchase #4 $217.77   12.611%   $245.233   $245.23   $245.25   $245.20  
  Purchase #5 $134.41   12.779%   $151.5863   $151.59   $151.60   $151.60  
  Purchase #6 $222.36   13.513%   $252.4075   $252.41   $252.40   $252.40  
  Purchase #7 $47.81   6.227%   $50.7871   $50.79   $50.80   $50.80  
  7 purchase totals = $1,064.31       $1,170.8350   $1,170.84   $1,170.85   $1,170.90