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	$38.33	6.870%	$40.9633	$40.96	$40.95	$41.00
Purchase #2	$167.27	4.370%	$174.5797	$174.58	$174.60	$174.60
Purchase #3	$38.90	3.390%	$40.2187	$40.22	$40.20	$40.20
Purchase #4	$52.51	5.177%	$55.2284	$55.23	$55.25	$55.20
Purchase #5	$148.68	5.120%	$156.2924	$156.29	$156.30	$156.30
Purchase #6	$167.63	12.581%	$188.7195	$188.72	$188.70	$188.70
Purchase #7	$124.91	9.809%	$137.1624	$137.16	$137.15	$137.20
7 purchase totals =	$738.23		$793.1644	$793.16	$793.15	$793.20