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 $226.58   8.397%   $245.6059   $245.61   $245.60   $245.60  
  Purchase #2 $127.88   4.601%   $133.7638   $133.76   $133.75   $133.80  
  Purchase #3 $219.48   11.274%   $244.2242   $244.22   $244.20   $244.20  
  Purchase #4 $235.87   7.119%   $252.6616   $252.66   $252.65   $252.70  
  Purchase #5 $194.28   11.846%   $217.2944   $217.29   $217.30   $217.30  
  Purchase #6 $233.71   4.430%   $244.0634   $244.06   $244.05   $244.10  
  Purchase #7 $116.66   9.680%   $127.9527   $127.95   $127.95   $128.00  
  7 purchase totals = $1,354.46       $1,465.5660   $1,465.55   $1,465.50   $1,465.70