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	$234.64	7.238%	$251.6232	$251.62	$251.60	$251.60
Purchase #2	$157.97	9.774%	$173.41	$173.41	$173.40	$173.40
Purchase #3	$85.77	12.302%	$96.3214	$96.32	$96.30	$96.30
Purchase #4	$104.52	4.624%	$109.353	$109.35	$109.35	$109.40
Purchase #5	$215.83	6.223%	$229.2611	$229.26	$229.25	$229.30
Purchase #6	$134.46	4.530%	$140.551	$140.55	$140.55	$140.60
Purchase #7	$86.36	3.725%	$89.5769	$89.58	$89.60	$89.60
7 purchase totals =	$1,019.55		$1,090.0966	$1,090.09	$1,090.05	$1,090.20