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	$53.38	13.347%	$60.5046	$60.50	$60.50	$60.50
Purchase #2	$229.57	6.421%	$244.3107	$244.31	$244.30	$244.30
Purchase #3	$119.33	12.169%	$133.8513	$133.85	$133.85	$133.90
Purchase #4	$54.52	10.500%	$60.2446	$60.24	$60.25	$60.20
Purchase #5	$42.72	5.682%	$45.1474	$45.15	$45.15	$45.10
Purchase #6	$53.69	12.812%	$60.5688	$60.57	$60.55	$60.60
Purchase #7	$210.41	13.715%	$239.2677	$239.27	$239.25	$239.30
7 purchase totals =	$763.62		$843.8951	$843.89	$843.85	$843.90