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	$51.25	13.157%	$57.993	$57.99	$58.00	$58.00
Purchase #2	$147.92	6.695%	$157.8232	$157.82	$157.80	$157.80
Purchase #3	$199.83	11.770%	$223.35	$223.35	$223.35	$223.40
Purchase #4	$103.83	7.418%	$111.5321	$111.53	$111.55	$111.50
Purchase #5	$37.95	11.144%	$42.1791	$42.18	$42.20	$42.20
Purchase #6	$112.79	12.864%	$127.2993	$127.30	$127.30	$127.30
Purchase #7	$53.38	12.115%	$59.847	$59.85	$59.85	$59.80
7 purchase totals =	$706.95		$780.0237	$780.02	$780.05	$780.00