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	$111.85	3.578%	$115.852	$115.85	$115.85	$115.90
Purchase #2	$91.84	12.240%	$103.0812	$103.08	$103.10	$103.10
Purchase #3	$45.41	5.392%	$47.8585	$47.86	$47.85	$47.90
Purchase #4	$155.61	6.706%	$166.0452	$166.05	$166.05	$166.00
Purchase #5	$30.59	11.367%	$34.0672	$34.07	$34.05	$34.10
Purchase #6	$77.84	7.549%	$83.7161	$83.72	$83.70	$83.70
Purchase #7	$86.60	11.152%	$96.2576	$96.26	$96.25	$96.30
7 purchase totals =	$599.74		$646.8778	$646.89	$646.85	$647.00