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	$162.47	3.600%	$168.3189	$168.32	$168.30	$168.30
Purchase #2	$98.76	12.677%	$111.2798	$111.28	$111.30	$111.30
Purchase #3	$127.82	8.531%	$138.7243	$138.72	$138.70	$138.70
Purchase #4	$168.35	8.536%	$182.7204	$182.72	$182.70	$182.70
Purchase #5	$137.82	8.562%	$149.6201	$149.62	$149.60	$149.60
Purchase #6	$166.55	4.560%	$174.1447	$174.14	$174.15	$174.10
Purchase #7	$159.40	13.443%	$180.8281	$180.83	$180.85	$180.80
7 purchase totals =	$1,021.17		$1,105.6363	$1,105.63	$1,105.60	$1,105.50