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	$108.60	9.190%	$118.5803	$118.58	$118.60	$118.60
Purchase #2	$31.85	4.823%	$33.3861	$33.39	$33.40	$33.40
Purchase #3	$83.41	8.582%	$90.5682	$90.57	$90.55	$90.60
Purchase #4	$164.63	4.692%	$172.3544	$172.35	$172.35	$172.40
Purchase #5	$125.36	3.751%	$130.0623	$130.06	$130.05	$130.10
Purchase #6	$33.68	10.639%	$37.2632	$37.26	$37.25	$37.30
Purchase #7	$150.73	5.515%	$159.0428	$159.04	$159.05	$159.00
7 purchase totals =	$698.26		$741.2573	$741.25	$741.25	$741.40