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	$79.84	7.435%	$85.7761	$85.78	$85.80	$85.80
Purchase #2	$90.67	4.360%	$94.6232	$94.62	$94.60	$94.60
Purchase #3	$171.86	12.745%	$193.7636	$193.76	$193.75	$193.80
Purchase #4	$28.79	13.379%	$32.6418	$32.64	$32.65	$32.60
Purchase #5	$123.61	12.494%	$139.0538	$139.05	$139.05	$139.10
Purchase #6	$182.91	11.298%	$203.5752	$203.58	$203.60	$203.60
Purchase #7	$122.80	4.148%	$127.8937	$127.89	$127.90	$127.90
7 purchase totals =	$800.48		$877.3274	$877.32	$877.35	$877.40