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	$99.37	12.576%	$111.8668	$111.87	$111.85	$111.90
Purchase #2	$202.57	3.364%	$209.3845	$209.38	$209.40	$209.40
Purchase #3	$54.31	4.150%	$56.5639	$56.56	$56.55	$56.60
Purchase #4	$51.32	7.333%	$55.0833	$55.08	$55.10	$55.10
Purchase #5	$30.90	13.752%	$35.1494	$35.15	$35.15	$35.10
Purchase #6	$65.86	7.360%	$70.7073	$70.71	$70.70	$70.70
Purchase #7	$131.92	9.568%	$144.5421	$144.54	$144.55	$144.50
7 purchase totals =	$636.25		$683.2973	$683.29	$683.30	$683.30