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	$132.55	5.312%	$139.5911	$139.59	$139.60	$139.60
Purchase #2	$219.38	3.744%	$227.5936	$227.59	$227.60	$227.60
Purchase #3	$224.69	4.830%	$235.5425	$235.54	$235.55	$235.50
Purchase #4	$50.70	4.654%	$53.0596	$53.06	$53.05	$53.10
Purchase #5	$200.51	3.854%	$208.2377	$208.24	$208.25	$208.20
Purchase #6	$206.59	4.430%	$215.7419	$215.74	$215.75	$215.70
Purchase #7	$57.38	7.551%	$61.7128	$61.71	$61.70	$61.70
7 purchase totals =	$1,091.80		$1,141.4792	$1,141.47	$1,141.50	$1,141.40