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	$6.56	13.297%	$7.4323	$7.43	$7.45	$7.40
Purchase #2	$189.72	7.405%	$203.7688	$203.77	$203.75	$203.80
Purchase #3	$26.93	9.742%	$29.5535	$29.55	$29.55	$29.60
Purchase #4	$166.47	8.215%	$180.1455	$180.15	$180.15	$180.10
Purchase #5	$66.91	6.295%	$71.122	$71.12	$71.10	$71.10
Purchase #6	$219.53	4.348%	$229.0752	$229.08	$229.10	$229.10
Purchase #7	$53.89	11.217%	$59.9348	$59.93	$59.95	$59.90
7 purchase totals =	$730.01		$781.0321	$781.03	$781.05	$781.00