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	$33.55	3.661%	$34.7783	$34.78	$34.80	$34.80
Purchase #2	$196.45	13.537%	$223.0434	$223.04	$223.05	$223.00
Purchase #3	$59.31	11.124%	$65.9076	$65.91	$65.90	$65.90
Purchase #4	$222.31	3.323%	$229.6974	$229.70	$229.70	$229.70
Purchase #5	$194.51	7.660%	$209.4095	$209.41	$209.40	$209.40
Purchase #6	$17.77	11.543%	$19.8212	$19.82	$19.80	$19.80
Purchase #7	$52.88	6.702%	$56.424	$56.42	$56.40	$56.40
7 purchase totals =	$776.78		$839.0814	$839.08	$839.05	$839.00