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	$151.33	10.311%	$166.9336	$166.93	$166.95	$166.90
Purchase #2	$171.61	9.818%	$188.4587	$188.46	$188.45	$188.50
Purchase #3	$51.77	11.800%	$57.8789	$57.88	$57.90	$57.90
Purchase #4	$21.59	7.259%	$23.1572	$23.16	$23.15	$23.20
Purchase #5	$53.72	6.275%	$57.0909	$57.09	$57.10	$57.10
Purchase #6	$89.89	9.198%	$98.1581	$98.16	$98.15	$98.20
Purchase #7	$230.69	10.288%	$254.4234	$254.42	$254.40	$254.40
7 purchase totals =	$770.60		$846.1008	$846.10	$846.10	$846.20