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	$131.66	5.468%	$138.8592	$138.86	$138.85	$138.90
Purchase #2	$76.48	3.809%	$79.3931	$79.39	$79.40	$79.40
Purchase #3	$37.46	5.624%	$39.5668	$39.57	$39.55	$39.60
Purchase #4	$6.31	8.764%	$6.863	$6.86	$6.85	$6.90
Purchase #5	$130.74	9.834%	$143.597	$143.60	$143.60	$143.60
Purchase #6	$158.34	9.118%	$172.7774	$172.78	$172.80	$172.80
Purchase #7	$42.74	7.181%	$45.8092	$45.81	$45.80	$45.80
7 purchase totals =	$583.73		$626.8657	$626.87	$626.85	$627.00