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	$178.72	3.503%	$184.9806	$184.98	$185.00	$185.00
Purchase #2	$49.45	8.566%	$53.6859	$53.69	$53.70	$53.70
Purchase #3	$50.92	4.815%	$53.3718	$53.37	$53.35	$53.40
Purchase #4	$48.96	12.190%	$54.9282	$54.93	$54.95	$54.90
Purchase #5	$70.28	13.855%	$80.0173	$80.02	$80.00	$80.00
Purchase #6	$235.44	5.349%	$248.0337	$248.03	$248.05	$248.00
Purchase #7	$192.72	11.831%	$215.5207	$215.52	$215.50	$215.50
7 purchase totals =	$826.49		$890.5382	$890.54	$890.55	$890.50