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	$66.68	13.639%	$75.7745	$75.77	$75.75	$75.80
Purchase #2	$245.44	12.299%	$275.6267	$275.63	$275.65	$275.60
Purchase #3	$127.36	12.742%	$143.5882	$143.59	$143.60	$143.60
Purchase #4	$87.76	3.606%	$90.9246	$90.92	$90.90	$90.90
Purchase #5	$18.96	11.128%	$21.0699	$21.07	$21.05	$21.10
Purchase #6	$5.42	12.360%	$6.0899	$6.09	$6.10	$6.10
Purchase #7	$96.54	4.389%	$100.7771	$100.78	$100.80	$100.80
7 purchase totals =	$648.16		$713.8509	$713.85	$713.85	$713.90