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	$82.82	9.278%	$90.504	$90.50	$90.50	$90.50
Purchase #2	$214.54	12.432%	$241.2116	$241.21	$241.20	$241.20
Purchase #3	$57.96	4.728%	$60.7003	$60.70	$60.70	$60.70
Purchase #4	$62.37	7.285%	$66.9137	$66.91	$66.90	$66.90
Purchase #5	$218.38	11.389%	$243.2513	$243.25	$243.25	$243.30
Purchase #6	$129.25	6.158%	$137.2092	$137.21	$137.20	$137.20
Purchase #7	$161.52	11.568%	$180.2046	$180.20	$180.20	$180.20
7 purchase totals =	$926.84		$1,019.9947	$1,019.98	$1,019.95	$1,020.00