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	$6.38	8.286%	$6.9086	$6.91	$6.90	$6.90
Purchase #2	$225.72	3.835%	$234.3764	$234.38	$234.40	$234.40
Purchase #3	$228.82	11.842%	$255.9169	$255.92	$255.90	$255.90
Purchase #4	$74.46	3.631%	$77.1636	$77.16	$77.15	$77.20
Purchase #5	$208.88	5.259%	$219.865	$219.87	$219.85	$219.90
Purchase #6	$13.91	6.675%	$14.8385	$14.84	$14.85	$14.80
Purchase #7	$93.35	12.851%	$105.3464	$105.35	$105.35	$105.30
7 purchase totals =	$851.52		$914.4154	$914.43	$914.40	$914.40