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	$83.96	9.325%	$91.7893	$91.79	$91.80	$91.80
Purchase #2	$124.84	9.566%	$136.7822	$136.78	$136.80	$136.80
Purchase #3	$105.42	8.301%	$114.1709	$114.17	$114.15	$114.20
Purchase #4	$63.73	5.620%	$67.3116	$67.31	$67.30	$67.30
Purchase #5	$127.32	4.858%	$133.5052	$133.51	$133.50	$133.50
Purchase #6	$73.84	6.754%	$78.8272	$78.83	$78.85	$78.80
Purchase #7	$127.39	11.419%	$141.9367	$141.94	$141.95	$141.90
7 purchase totals =	$706.50		$764.3231	$764.33	$764.35	$764.30