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	$32.87	4.493%	$34.3468	$34.35	$34.35	$34.30
Purchase #2	$134.94	3.730%	$139.9733	$139.97	$139.95	$140.00
Purchase #3	$96.75	12.674%	$109.0121	$109.01	$109.00	$109.00
Purchase #4	$208.56	13.483%	$236.6801	$236.68	$236.70	$236.70
Purchase #5	$77.67	10.399%	$85.7469	$85.75	$85.75	$85.70
Purchase #6	$79.61	12.552%	$89.6026	$89.60	$89.60	$89.60
Purchase #7	$97.77	11.845%	$109.3509	$109.35	$109.35	$109.40
7 purchase totals =	$728.17		$804.7127	$804.71	$804.70	$804.70