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	$45.63	6.179%	$48.4495	$48.45	$48.45	$48.40
Purchase #2	$209.75	11.749%	$234.3935	$234.39	$234.40	$234.40
Purchase #3	$20.28	13.324%	$22.9821	$22.98	$23.00	$23.00
Purchase #4	$15.80	9.248%	$17.2612	$17.26	$17.25	$17.30
Purchase #5	$86.39	3.765%	$89.6426	$89.64	$89.65	$89.60
Purchase #6	$75.30	4.346%	$78.5725	$78.57	$78.55	$78.60
Purchase #7	$233.45	4.742%	$244.5202	$244.52	$244.50	$244.50
7 purchase totals =	$686.60		$735.8216	$735.81	$735.80	$735.80