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	$34.27	4.584%	$35.8409	$35.84	$35.85	$35.80
Purchase #2	$85.65	4.868%	$89.8194	$89.82	$89.80	$89.80
Purchase #3	$204.78	11.309%	$227.9386	$227.94	$227.95	$227.90
Purchase #4	$209.58	11.206%	$233.0655	$233.07	$233.05	$233.10
Purchase #5	$13.58	10.554%	$15.0132	$15.01	$15.00	$15.00
Purchase #6	$186.62	10.457%	$206.1349	$206.13	$206.15	$206.10
Purchase #7	$48.64	11.327%	$54.1495	$54.15	$54.15	$54.10
7 purchase totals =	$783.12		$861.9620	$861.96	$861.95	$861.80