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	$150.54	13.649%	$171.0872	$171.09	$171.10	$171.10
Purchase #2	$41.54	4.386%	$43.3619	$43.36	$43.35	$43.40
Purchase #3	$42.56	12.157%	$47.734	$47.73	$47.75	$47.70
Purchase #4	$224.25	8.367%	$243.013	$243.01	$243.00	$243.00
Purchase #5	$57.83	11.643%	$64.5631	$64.56	$64.55	$64.60
Purchase #6	$34.37	4.412%	$35.8864	$35.89	$35.90	$35.90
Purchase #7	$205.42	8.868%	$223.6366	$223.64	$223.65	$223.60
7 purchase totals =	$756.51		$829.2822	$829.28	$829.30	$829.30