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	$210.52	8.375%	$228.1511	$228.15	$228.15	$228.20
Purchase #2	$211.58	13.510%	$240.1645	$240.16	$240.15	$240.20
Purchase #3	$59.41	12.590%	$66.8897	$66.89	$66.90	$66.90
Purchase #4	$85.26	4.577%	$89.1624	$89.16	$89.15	$89.20
Purchase #5	$132.35	3.299%	$136.7162	$136.72	$136.70	$136.70
Purchase #6	$16.46	13.131%	$18.6214	$18.62	$18.60	$18.60
Purchase #7	$73.90	4.713%	$77.3829	$77.38	$77.40	$77.40
7 purchase totals =	$789.48		$857.0882	$857.08	$857.05	$857.20