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	$166.79	11.214%	$185.4938	$185.49	$185.50	$185.50
Purchase #2	$205.56	10.145%	$226.4141	$226.41	$226.40	$226.40
Purchase #3	$174.89	9.587%	$191.6567	$191.66	$191.65	$191.70
Purchase #4	$137.65	9.827%	$151.1769	$151.18	$151.20	$151.20
Purchase #5	$134.69	6.554%	$143.5176	$143.52	$143.50	$143.50
Purchase #6	$31.58	13.581%	$35.8689	$35.87	$35.85	$35.90
Purchase #7	$191.30	11.679%	$213.6419	$213.64	$213.65	$213.60
7 purchase totals =	$1,042.46		$1,147.7699	$1,147.77	$1,147.75	$1,147.80