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	$240.53	9.116%	$262.4567	$262.46	$262.45	$262.50
Purchase #2	$218.75	4.806%	$229.2631	$229.26	$229.25	$229.30
Purchase #3	$156.72	9.804%	$172.0848	$172.08	$172.10	$172.10
Purchase #4	$39.55	6.747%	$42.2184	$42.22	$42.20	$42.20
Purchase #5	$204.33	11.295%	$227.4091	$227.41	$227.40	$227.40
Purchase #6	$183.98	8.813%	$200.1942	$200.19	$200.20	$200.20
Purchase #7	$127.38	7.366%	$136.7628	$136.76	$136.75	$136.80
7 purchase totals =	$1,171.24		$1,270.3891	$1,270.38	$1,270.35	$1,270.50