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	$230.94	3.334%	$238.6395	$238.64	$238.65	$238.60
Purchase #2	$38.68	13.171%	$43.7745	$43.77	$43.75	$43.80
Purchase #3	$77.25	10.431%	$85.3079	$85.31	$85.30	$85.30
Purchase #4	$211.62	12.588%	$238.2587	$238.26	$238.25	$238.30
Purchase #5	$79.85	13.792%	$90.8629	$90.86	$90.85	$90.90
Purchase #6	$140.48	11.804%	$157.0623	$157.06	$157.05	$157.10
Purchase #7	$96.33	10.859%	$106.7905	$106.79	$106.80	$106.80
7 purchase totals =	$875.15		$960.6963	$960.69	$960.65	$960.80