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	$33.63	4.565%	$35.1652	$35.17	$35.15	$35.20
Purchase #2	$83.55	13.393%	$94.7399	$94.74	$94.75	$94.70
Purchase #3	$19.35	4.612%	$20.2424	$20.24	$20.25	$20.20
Purchase #4	$223.52	6.621%	$238.3193	$238.32	$238.30	$238.30
Purchase #5	$150.30	9.294%	$164.2689	$164.27	$164.25	$164.30
Purchase #6	$117.65	11.108%	$130.7186	$130.72	$130.70	$130.70
Purchase #7	$124.50	13.437%	$141.2291	$141.23	$141.25	$141.20
7 purchase totals =	$752.50		$824.6834	$824.69	$824.65	$824.60