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	$20.99	6.390%	$22.3313	$22.33	$22.35	$22.30
Purchase #2	$114.40	4.586%	$119.6464	$119.65	$119.65	$119.60
Purchase #3	$12.75	5.765%	$13.485	$13.49	$13.50	$13.50
Purchase #4	$141.54	6.804%	$151.1704	$151.17	$151.15	$151.20
Purchase #5	$151.25	3.163%	$156.034	$156.03	$156.05	$156.00
Purchase #6	$154.63	8.506%	$167.7828	$167.78	$167.80	$167.80
Purchase #7	$136.98	4.313%	$142.8879	$142.89	$142.90	$142.90
7 purchase totals =	$732.54		$773.3378	$773.34	$773.40	$773.30