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	$102.88	5.460%	$108.4972	$108.50	$108.50	$108.50
Purchase #2	$79.39	3.788%	$82.3973	$82.40	$82.40	$82.40
Purchase #3	$16.68	12.847%	$18.8229	$18.82	$18.80	$18.80
Purchase #4	$92.80	6.857%	$99.1633	$99.16	$99.15	$99.20
Purchase #5	$190.29	10.607%	$210.4741	$210.47	$210.45	$210.50
Purchase #6	$109.80	4.156%	$114.3633	$114.36	$114.35	$114.40
Purchase #7	$150.34	3.306%	$155.3102	$155.31	$155.30	$155.30
7 purchase totals =	$742.18		$789.0283	$789.02	$788.95	$789.10