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 $221.89   11.852%   $248.1884   $248.19   $248.20   $248.20  
  Purchase #2 $129.72   3.804%   $134.6545   $134.65   $134.65   $134.70  
  Purchase #3 $188.42   3.455%   $194.9299   $194.93   $194.95   $194.90  
  Purchase #4 $183.78   6.584%   $195.8801   $195.88   $195.90   $195.90  
  Purchase #5 $122.68   6.330%   $130.4456   $130.45   $130.45   $130.40  
  Purchase #6 $196.77   6.740%   $210.0323   $210.03   $210.05   $210.00  
  Purchase #7 $218.80   12.380%   $245.8874   $245.89   $245.90   $245.90  
  7 purchase totals = $1,262.06       $1,360.0182   $1,360.02   $1,360.10   $1,360.00