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	$15.38	10.785%	$17.0387	$17.04	$17.05	$17.00
Purchase #2	$90.47	10.309%	$99.7966	$99.80	$99.80	$99.80
Purchase #3	$77.64	8.124%	$83.9475	$83.95	$83.95	$83.90
Purchase #4	$19.32	6.618%	$20.5986	$20.60	$20.60	$20.60
Purchase #5	$80.54	10.456%	$88.9613	$88.96	$88.95	$89.00
Purchase #6	$99.39	4.120%	$103.4849	$103.48	$103.50	$103.50
Purchase #7	$229.70	11.775%	$256.7472	$256.75	$256.75	$256.70
7 purchase totals =	$612.44		$670.5748	$670.58	$670.60	$670.50