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	$24.37	13.468%	$27.6522	$27.65	$27.65	$27.70
Purchase #2	$31.95	11.311%	$35.5639	$35.56	$35.55	$35.60
Purchase #3	$83.89	5.628%	$88.6113	$88.61	$88.60	$88.60
Purchase #4	$202.52	7.119%	$216.9374	$216.94	$216.95	$216.90
Purchase #5	$132.41	6.589%	$141.1345	$141.13	$141.15	$141.10
Purchase #6	$97.88	7.628%	$105.3463	$105.35	$105.35	$105.30
Purchase #7	$160.84	3.580%	$166.5981	$166.60	$166.60	$166.60
7 purchase totals =	$733.86		$781.8437	$781.84	$781.85	$781.80