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	$77.41	8.109%	$83.6872	$83.69	$83.70	$83.70
Purchase #2	$87.94	12.575%	$98.9985	$99.00	$99.00	$99.00
Purchase #3	$189.51	11.467%	$211.2411	$211.24	$211.25	$211.20
Purchase #4	$70.70	11.156%	$78.5873	$78.59	$78.60	$78.60
Purchase #5	$122.58	9.190%	$133.8451	$133.85	$133.85	$133.80
Purchase #6	$44.67	12.740%	$50.361	$50.36	$50.35	$50.40
Purchase #7	$51.78	11.423%	$57.6948	$57.69	$57.70	$57.70
7 purchase totals =	$644.59		$714.4150	$714.42	$714.45	$714.40