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	$81.25	11.375%	$90.4922	$90.49	$90.50	$90.50
Purchase #2	$117.52	4.863%	$123.235	$123.24	$123.25	$123.20
Purchase #3	$68.72	7.419%	$73.8183	$73.82	$73.80	$73.80
Purchase #4	$115.94	4.221%	$120.8338	$120.83	$120.85	$120.80
Purchase #5	$25.93	7.802%	$27.9531	$27.95	$27.95	$28.00
Purchase #6	$106.89	4.335%	$111.5237	$111.52	$111.50	$111.50
Purchase #7	$30.72	8.337%	$33.2811	$33.28	$33.30	$33.30
7 purchase totals =	$546.97		$581.1372	$581.13	$581.15	$581.10