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	$111.86	7.520%	$120.2719	$120.27	$120.25	$120.30
Purchase #2	$11.61	4.608%	$12.145	$12.15	$12.15	$12.10
Purchase #3	$234.46	10.799%	$259.7793	$259.78	$259.80	$259.80
Purchase #4	$7.48	11.169%	$8.3154	$8.32	$8.30	$8.30
Purchase #5	$228.50	4.738%	$239.3263	$239.33	$239.35	$239.30
Purchase #6	$66.61	8.113%	$72.0141	$72.01	$72.00	$72.00
Purchase #7	$209.86	6.538%	$223.5806	$223.58	$223.60	$223.60
7 purchase totals =	$870.38		$935.4326	$935.44	$935.45	$935.40