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	$233.37	7.295%	$250.3943	$250.39	$250.40	$250.40
Purchase #2	$69.28	3.731%	$71.8648	$71.86	$71.85	$71.90
Purchase #3	$32.69	12.313%	$36.7151	$36.72	$36.70	$36.70
Purchase #4	$78.62	8.276%	$85.1266	$85.13	$85.15	$85.10
Purchase #5	$78.78	11.713%	$88.0075	$88.01	$88.00	$88.00
Purchase #6	$127.79	13.665%	$145.2525	$145.25	$145.25	$145.30
Purchase #7	$140.32	4.138%	$146.1264	$146.13	$146.15	$146.10
7 purchase totals =	$760.85		$823.4872	$823.49	$823.50	$823.50