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	$83.71	6.666%	$89.2901	$89.29	$89.30	$89.30
Purchase #2	$13.85	8.585%	$15.039	$15.04	$15.05	$15.00
Purchase #3	$240.26	5.428%	$253.3013	$253.30	$253.30	$253.30
Purchase #4	$236.50	4.757%	$247.7503	$247.75	$247.75	$247.80
Purchase #5	$65.41	11.464%	$72.9086	$72.91	$72.90	$72.90
Purchase #6	$244.78	6.152%	$259.8389	$259.84	$259.85	$259.80
Purchase #7	$246.84	3.139%	$254.5883	$254.59	$254.60	$254.60
7 purchase totals =	$1,131.35		$1,192.7165	$1,192.72	$1,192.75	$1,192.70