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	$78.61	5.306%	$82.781	$82.78	$82.80	$82.80
Purchase #2	$99.66	12.531%	$112.1484	$112.15	$112.15	$112.10
Purchase #3	$6.31	7.833%	$6.8043	$6.80	$6.80	$6.80
Purchase #4	$155.63	7.149%	$166.756	$166.76	$166.75	$166.80
Purchase #5	$40.38	5.572%	$42.63	$42.63	$42.65	$42.60
Purchase #6	$226.94	5.148%	$238.6229	$238.62	$238.60	$238.60
Purchase #7	$77.30	11.768%	$86.3967	$86.40	$86.40	$86.40
7 purchase totals =	$684.83		$736.1393	$736.14	$736.15	$736.10