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	$136.76	12.487%	$153.8372	$153.84	$153.85	$153.80
Purchase #2	$174.60	6.266%	$185.5404	$185.54	$185.55	$185.50
Purchase #3	$66.61	3.279%	$68.7941	$68.79	$68.80	$68.80
Purchase #4	$242.35	5.562%	$255.8295	$255.83	$255.85	$255.80
Purchase #5	$148.81	10.247%	$164.0586	$164.06	$164.05	$164.10
Purchase #6	$243.52	11.700%	$272.0118	$272.01	$272.00	$272.00
Purchase #7	$17.66	13.866%	$20.1087	$20.11	$20.10	$20.10
7 purchase totals =	$1,030.31		$1,120.1803	$1,120.18	$1,120.20	$1,120.10