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	$118.91	13.798%	$135.3172	$135.32	$135.30	$135.30
Purchase #2	$97.78	4.811%	$102.4842	$102.48	$102.50	$102.50
Purchase #3	$190.42	13.394%	$215.9249	$215.92	$215.90	$215.90
Purchase #4	$228.45	9.504%	$250.1619	$250.16	$250.15	$250.20
Purchase #5	$18.76	6.808%	$20.0372	$20.04	$20.05	$20.00
Purchase #6	$222.77	9.707%	$244.3943	$244.39	$244.40	$244.40
Purchase #7	$175.51	4.435%	$183.2939	$183.29	$183.30	$183.30
7 purchase totals =	$1,052.60		$1,151.6136	$1,151.60	$1,151.60	$1,151.60