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	$35.99	7.757%	$38.7817	$38.78	$38.80	$38.80
Purchase #2	$66.40	9.271%	$72.5559	$72.56	$72.55	$72.60
Purchase #3	$128.44	10.127%	$141.4471	$141.45	$141.45	$141.40
Purchase #4	$48.94	8.709%	$53.2022	$53.20	$53.20	$53.20
Purchase #5	$129.41	11.644%	$144.4785	$144.48	$144.50	$144.50
Purchase #6	$161.62	11.598%	$180.3647	$180.36	$180.35	$180.40
Purchase #7	$153.58	7.472%	$165.0555	$165.06	$165.05	$165.10
7 purchase totals =	$724.38		$795.8856	$795.89	$795.90	$796.00