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	$116.55	5.607%	$123.085	$123.09	$123.10	$123.10
Purchase #2	$48.54	12.127%	$54.4264	$54.43	$54.45	$54.40
Purchase #3	$5.89	9.558%	$6.453	$6.45	$6.45	$6.50
Purchase #4	$240.50	3.255%	$248.3283	$248.33	$248.35	$248.30
Purchase #5	$63.73	10.298%	$70.2929	$70.29	$70.30	$70.30
Purchase #6	$90.46	6.718%	$96.5371	$96.54	$96.55	$96.50
Purchase #7	$223.73	13.750%	$254.4929	$254.49	$254.50	$254.50
7 purchase totals =	$789.40		$853.6156	$853.62	$853.70	$853.60