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	$136.50	13.165%	$154.4702	$154.47	$154.45	$154.50
Purchase #2	$105.89	3.295%	$109.3791	$109.38	$109.40	$109.40
Purchase #3	$9.47	6.256%	$10.0624	$10.06	$10.05	$10.10
Purchase #4	$88.42	4.704%	$92.5793	$92.58	$92.60	$92.60
Purchase #5	$33.27	5.373%	$35.0576	$35.06	$35.05	$35.10
Purchase #6	$96.40	6.618%	$102.7798	$102.78	$102.80	$102.80
Purchase #7	$49.80	11.253%	$55.404	$55.40	$55.40	$55.40
7 purchase totals =	$519.75		$559.7324	$559.73	$559.75	$559.90