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	$90.67	10.358%	$100.0616	$100.06	$100.05	$100.10
Purchase #2	$229.97	7.607%	$247.4638	$247.46	$247.45	$247.50
Purchase #3	$151.28	10.392%	$167.001	$167.00	$167.00	$167.00
Purchase #4	$130.40	4.713%	$136.5458	$136.55	$136.55	$136.50
Purchase #5	$38.74	4.306%	$40.4081	$40.41	$40.40	$40.40
Purchase #6	$123.67	11.836%	$138.3076	$138.31	$138.30	$138.30
Purchase #7	$38.78	11.302%	$43.1629	$43.16	$43.15	$43.20
7 purchase totals =	$803.51		$872.9508	$872.95	$872.90	$873.00