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	$114.95	11.568%	$128.2474	$128.25	$128.25	$128.20
Purchase #2	$191.30	9.472%	$209.4199	$209.42	$209.40	$209.40
Purchase #3	$10.66	4.631%	$11.1537	$11.15	$11.15	$11.20
Purchase #4	$63.39	13.646%	$72.0402	$72.04	$72.05	$72.00
Purchase #5	$94.81	5.276%	$99.8122	$99.81	$99.80	$99.80
Purchase #6	$67.33	7.264%	$72.2209	$72.22	$72.20	$72.20
Purchase #7	$45.63	6.391%	$48.5462	$48.55	$48.55	$48.50
7 purchase totals =	$588.07		$641.4405	$641.44	$641.40	$641.30