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	$45.43	11.242%	$50.5372	$50.54	$50.55	$50.50
Purchase #2	$156.40	10.467%	$172.7704	$172.77	$172.75	$172.80
Purchase #3	$178.60	9.560%	$195.6742	$195.67	$195.65	$195.70
Purchase #4	$9.87	5.235%	$10.3867	$10.39	$10.40	$10.40
Purchase #5	$166.89	8.399%	$180.9071	$180.91	$180.90	$180.90
Purchase #6	$64.33	7.279%	$69.0126	$69.01	$69.00	$69.00
Purchase #7	$102.40	3.136%	$105.6113	$105.61	$105.60	$105.60
7 purchase totals =	$723.92		$784.8995	$784.90	$784.85	$784.90