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	$65.89	5.447%	$69.479	$69.48	$69.50	$69.50
Purchase #2	$165.55	12.139%	$185.6461	$185.65	$185.65	$185.60
Purchase #3	$123.76	3.539%	$128.1399	$128.14	$128.15	$128.10
Purchase #4	$44.62	8.211%	$48.2837	$48.28	$48.30	$48.30
Purchase #5	$213.37	11.808%	$238.5647	$238.56	$238.55	$238.60
Purchase #6	$182.34	12.871%	$205.809	$205.81	$205.80	$205.80
Purchase #7	$29.65	8.792%	$32.2568	$32.26	$32.25	$32.30
7 purchase totals =	$825.18		$908.1792	$908.18	$908.20	$908.20