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 $217.76   12.839%   $245.7182   $245.72   $245.70   $245.70  
  Purchase #2 $37.38   11.786%   $41.7856   $41.79   $41.80   $41.80  
  Purchase #3 $147.83   3.263%   $152.6537   $152.65   $152.65   $152.70  
  Purchase #4 $101.78   9.186%   $111.1295   $111.13   $111.15   $111.10  
  Purchase #5 $240.49   5.155%   $252.8873   $252.89   $252.90   $252.90  
  Purchase #6 $101.55   13.615%   $115.376   $115.38   $115.40   $115.40  
  Purchase #7 $174.60   4.448%   $182.3662   $182.37   $182.35   $182.40  
  7 purchase totals = $1,021.39       $1,101.9165   $1,101.93   $1,101.95   $1,102.00