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	$248.38	3.776%	$257.7588	$257.76	$257.75	$257.80
Purchase #2	$81.98	10.787%	$90.8232	$90.82	$90.80	$90.80
Purchase #3	$125.98	6.275%	$133.8852	$133.89	$133.90	$133.90
Purchase #4	$121.89	7.241%	$130.7161	$130.72	$130.70	$130.70
Purchase #5	$192.99	6.423%	$205.3857	$205.39	$205.40	$205.40
Purchase #6	$32.73	10.427%	$36.1428	$36.14	$36.15	$36.10
Purchase #7	$158.36	4.270%	$165.122	$165.12	$165.10	$165.10
7 purchase totals =	$962.31		$1,019.8338	$1,019.84	$1,019.80	$1,019.80