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	$230.95	11.775%	$258.1444	$258.14	$258.15	$258.10
Purchase #2	$44.25	13.612%	$50.2733	$50.27	$50.25	$50.30
Purchase #3	$148.34	12.392%	$166.7223	$166.72	$166.70	$166.70
Purchase #4	$88.81	9.131%	$96.9192	$96.92	$96.90	$96.90
Purchase #5	$171.98	5.753%	$181.874	$181.87	$181.85	$181.90
Purchase #6	$17.25	4.593%	$18.0423	$18.04	$18.05	$18.00
Purchase #7	$38.53	9.730%	$42.279	$42.28	$42.30	$42.30
7 purchase totals =	$740.11		$814.2545	$814.24	$814.20	$814.20