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	$152.98	4.114%	$159.2736	$159.27	$159.25	$159.30
Purchase #2	$140.50	4.280%	$146.5134	$146.51	$146.50	$146.50
Purchase #3	$58.78	6.321%	$62.4955	$62.50	$62.50	$62.50
Purchase #4	$139.81	3.593%	$144.8334	$144.83	$144.85	$144.80
Purchase #5	$10.77	7.294%	$11.5556	$11.56	$11.55	$11.60
Purchase #6	$182.76	5.506%	$192.8228	$192.82	$192.80	$192.80
Purchase #7	$30.93	3.674%	$32.0664	$32.07	$32.05	$32.10
7 purchase totals =	$716.53		$749.5607	$749.56	$749.50	$749.60