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 $185.95   10.149%   $204.8221   $204.82   $204.80   $204.80  
  Purchase #2 $32.93   3.632%   $34.126   $34.13   $34.15   $34.10  
  Purchase #3 $40.94   12.448%   $46.0362   $46.04   $46.05   $46.00  
  Purchase #4 $237.57   3.420%   $245.6949   $245.69   $245.70   $245.70  
  Purchase #5 $214.46   8.804%   $233.3411   $233.34   $233.35   $233.30  
  Purchase #6 $64.34   6.381%   $68.4455   $68.45   $68.45   $68.40  
  Purchase #7 $222.67   5.537%   $234.9992   $235.00   $235.00   $235.00  
  7 purchase totals = $998.86       $1,067.4650   $1,067.47   $1,067.50   $1,067.30