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	$37.47	4.497%	$39.155	$39.16	$39.15	$39.20
Purchase #2	$233.52	10.594%	$258.2591	$258.26	$258.25	$258.30
Purchase #3	$51.60	6.189%	$54.7935	$54.79	$54.80	$54.80
Purchase #4	$236.81	5.796%	$250.5355	$250.54	$250.55	$250.50
Purchase #5	$151.60	13.374%	$171.875	$171.88	$171.90	$171.90
Purchase #6	$235.97	6.464%	$251.2231	$251.22	$251.20	$251.20
Purchase #7	$110.53	4.556%	$115.5657	$115.57	$115.55	$115.60
7 purchase totals =	$1,057.50		$1,141.4069	$1,141.42	$1,141.40	$1,141.50