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	$40.67	4.436%	$42.4741	$42.47	$42.45	$42.50
Purchase #2	$223.37	9.442%	$244.4606	$244.46	$244.45	$244.50
Purchase #3	$107.32	4.486%	$112.1344	$112.13	$112.15	$112.10
Purchase #4	$84.67	13.417%	$96.0302	$96.03	$96.05	$96.00
Purchase #5	$166.57	11.532%	$185.7789	$185.78	$185.80	$185.80
Purchase #6	$238.43	10.659%	$263.8443	$263.84	$263.85	$263.80
Purchase #7	$33.93	3.564%	$35.1393	$35.14	$35.15	$35.10
7 purchase totals =	$894.96		$979.8618	$979.85	$979.90	$979.80