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	$33.81	6.205%	$35.9079	$35.91	$35.90	$35.90
Purchase #2	$158.72	6.135%	$168.4575	$168.46	$168.45	$168.50
Purchase #3	$81.67	8.462%	$88.5809	$88.58	$88.60	$88.60
Purchase #4	$202.39	10.510%	$223.6612	$223.66	$223.65	$223.70
Purchase #5	$72.30	7.734%	$77.8917	$77.89	$77.90	$77.90
Purchase #6	$176.85	13.244%	$200.272	$200.27	$200.25	$200.30
Purchase #7	$29.78	5.278%	$31.3518	$31.35	$31.35	$31.40
7 purchase totals =	$755.52		$826.1230	$826.12	$826.10	$826.30