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	$171.69	5.141%	$180.5166	$180.52	$180.50	$180.50
Purchase #2	$210.64	10.832%	$233.4565	$233.46	$233.45	$233.50
Purchase #3	$42.31	13.521%	$48.0307	$48.03	$48.05	$48.00
Purchase #4	$250.31	8.404%	$271.3461	$271.35	$271.35	$271.30
Purchase #5	$142.86	6.478%	$152.1145	$152.11	$152.10	$152.10
Purchase #6	$187.68	3.622%	$194.4778	$194.48	$194.50	$194.50
Purchase #7	$221.97	13.332%	$251.563	$251.56	$251.55	$251.60
7 purchase totals =	$1,227.46		$1,331.5052	$1,331.51	$1,331.50	$1,331.50