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	$238.69	4.871%	$250.3166	$250.32	$250.30	$250.30
Purchase #2	$156.40	11.203%	$173.9215	$173.92	$173.90	$173.90
Purchase #3	$231.74	10.313%	$255.6393	$255.64	$255.65	$255.60
Purchase #4	$162.95	13.618%	$185.1405	$185.14	$185.15	$185.10
Purchase #5	$21.67	10.102%	$23.8591	$23.86	$23.85	$23.90
Purchase #6	$34.63	8.504%	$37.5749	$37.57	$37.55	$37.60
Purchase #7	$145.28	11.734%	$162.3272	$162.33	$162.35	$162.30
7 purchase totals =	$991.36		$1,088.7791	$1,088.78	$1,088.75	$1,088.70