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	$70.51	9.641%	$77.3079	$77.31	$77.30	$77.30
Purchase #2	$170.52	6.298%	$181.2593	$181.26	$181.25	$181.30
Purchase #3	$185.25	9.845%	$203.4879	$203.49	$203.50	$203.50
Purchase #4	$159.70	6.359%	$169.8553	$169.86	$169.85	$169.90
Purchase #5	$225.87	3.419%	$233.5925	$233.59	$233.60	$233.60
Purchase #6	$114.60	12.493%	$128.917	$128.92	$128.90	$128.90
Purchase #7	$75.97	9.640%	$83.2935	$83.29	$83.30	$83.30
7 purchase totals =	$1,002.42		$1,077.7134	$1,077.72	$1,077.70	$1,077.80