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	$122.84	4.691%	$128.6024	$128.60	$128.60	$128.60
Purchase #2	$171.52	4.393%	$179.0549	$179.05	$179.05	$179.10
Purchase #3	$121.28	10.220%	$133.6748	$133.67	$133.65	$133.70
Purchase #4	$56.67	9.102%	$61.8281	$61.83	$61.85	$61.80
Purchase #5	$216.45	10.317%	$238.7811	$238.78	$238.80	$238.80
Purchase #6	$198.63	3.476%	$205.5344	$205.53	$205.55	$205.50
Purchase #7	$123.93	8.600%	$134.588	$134.59	$134.60	$134.60
7 purchase totals =	$1,011.32		$1,082.0637	$1,082.05	$1,082.10	$1,082.10