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	$84.66	6.490%	$90.1544	$90.15	$90.15	$90.20
Purchase #2	$160.86	9.603%	$176.3074	$176.31	$176.30	$176.30
Purchase #3	$85.97	5.520%	$90.7155	$90.72	$90.70	$90.70
Purchase #4	$182.48	13.833%	$207.7225	$207.72	$207.70	$207.70
Purchase #5	$49.37	12.227%	$55.4065	$55.41	$55.40	$55.40
Purchase #6	$100.83	13.435%	$114.3765	$114.38	$114.40	$114.40
Purchase #7	$33.90	5.135%	$35.6408	$35.64	$35.65	$35.60
7 purchase totals =	$698.07		$770.3236	$770.33	$770.30	$770.30