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	$74.80	3.756%	$77.6095	$77.61	$77.60	$77.60
Purchase #2	$229.52	11.352%	$255.5751	$255.58	$255.60	$255.60
Purchase #3	$207.32	13.747%	$235.8203	$235.82	$235.80	$235.80
Purchase #4	$230.47	3.206%	$237.8589	$237.86	$237.85	$237.90
Purchase #5	$86.92	4.160%	$90.5359	$90.54	$90.55	$90.50
Purchase #6	$141.42	9.642%	$155.0557	$155.06	$155.05	$155.10
Purchase #7	$88.41	9.296%	$96.6286	$96.63	$96.65	$96.60
7 purchase totals =	$1,058.86		$1,149.0840	$1,149.10	$1,149.10	$1,149.10