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	$90.99	3.210%	$93.9108	$93.91	$93.90	$93.90
Purchase #2	$158.98	8.338%	$172.2358	$172.24	$172.25	$172.20
Purchase #3	$148.99	12.641%	$167.8238	$167.82	$167.80	$167.80
Purchase #4	$70.74	10.591%	$78.2321	$78.23	$78.25	$78.20
Purchase #5	$18.27	9.552%	$20.0152	$20.02	$20.00	$20.00
Purchase #6	$249.54	10.437%	$275.5845	$275.58	$275.60	$275.60
Purchase #7	$100.62	5.267%	$105.9197	$105.92	$105.90	$105.90
7 purchase totals =	$838.13		$913.7219	$913.72	$913.70	$913.60