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	$56.30	7.250%	$60.3818	$60.38	$60.40	$60.40
Purchase #2	$131.55	11.851%	$147.14	$147.14	$147.15	$147.10
Purchase #3	$11.43	10.818%	$12.6665	$12.67	$12.65	$12.70
Purchase #4	$184.66	4.524%	$193.014	$193.01	$193.00	$193.00
Purchase #5	$198.60	9.685%	$217.8344	$217.83	$217.85	$217.80
Purchase #6	$72.40	8.228%	$78.3571	$78.36	$78.35	$78.40
Purchase #7	$95.44	3.798%	$99.0648	$99.06	$99.05	$99.10
7 purchase totals =	$750.38		$808.4586	$808.45	$808.45	$808.50