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	$102.86	13.667%	$116.9179	$116.92	$116.90	$116.90
Purchase #2	$89.98	10.276%	$99.2263	$99.23	$99.25	$99.20
Purchase #3	$101.46	9.593%	$111.1931	$111.19	$111.20	$111.20
Purchase #4	$95.25	3.824%	$98.8924	$98.89	$98.90	$98.90
Purchase #5	$27.52	11.786%	$30.7635	$30.76	$30.75	$30.80
Purchase #6	$186.29	13.281%	$211.0312	$211.03	$211.05	$211.00
Purchase #7	$128.40	10.168%	$141.4557	$141.46	$141.45	$141.50
7 purchase totals =	$731.76		$809.4801	$809.48	$809.50	$809.50