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	$88.82	12.332%	$99.7733	$99.77	$99.75	$99.80
Purchase #2	$202.59	8.535%	$219.8811	$219.88	$219.90	$219.90
Purchase #3	$190.66	11.715%	$212.9958	$213.00	$213.00	$213.00
Purchase #4	$155.50	7.559%	$167.2542	$167.25	$167.25	$167.30
Purchase #5	$26.78	13.499%	$30.395	$30.40	$30.40	$30.40
Purchase #6	$80.72	6.420%	$85.9022	$85.90	$85.90	$85.90
Purchase #7	$12.75	13.873%	$14.5188	$14.52	$14.50	$14.50
7 purchase totals =	$757.82		$830.7204	$830.72	$830.70	$830.80