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	$37.62	11.523%	$41.955	$41.96	$41.95	$42.00
Purchase #2	$208.26	5.116%	$218.9146	$218.91	$218.90	$218.90
Purchase #3	$99.52	13.357%	$112.8129	$112.81	$112.80	$112.80
Purchase #4	$179.46	8.236%	$194.2403	$194.24	$194.25	$194.20
Purchase #5	$191.83	9.711%	$210.4586	$210.46	$210.45	$210.50
Purchase #6	$59.88	7.699%	$64.4902	$64.49	$64.50	$64.50
Purchase #7	$80.42	12.517%	$90.4862	$90.49	$90.50	$90.50
7 purchase totals =	$856.99		$933.3578	$933.36	$933.35	$933.40