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	$88.79	13.279%	$100.5804	$100.58	$100.60	$100.60
Purchase #2	$107.45	10.182%	$118.3906	$118.39	$118.40	$118.40
Purchase #3	$133.64	10.743%	$147.9969	$148.00	$148.00	$148.00
Purchase #4	$98.37	9.600%	$107.8135	$107.81	$107.80	$107.80
Purchase #5	$101.36	4.431%	$105.8513	$105.85	$105.85	$105.90
Purchase #6	$92.83	6.450%	$98.8175	$98.82	$98.80	$98.80
Purchase #7	$55.81	11.261%	$62.0948	$62.09	$62.10	$62.10
7 purchase totals =	$678.25		$741.5450	$741.54	$741.55	$741.60