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	$250.39	11.139%	$278.2809	$278.28	$278.30	$278.30
Purchase #2	$176.86	13.558%	$200.8387	$200.84	$200.85	$200.80
Purchase #3	$223.86	11.709%	$250.0718	$250.07	$250.05	$250.10
Purchase #4	$156.71	6.630%	$167.0999	$167.10	$167.10	$167.10
Purchase #5	$67.46	10.575%	$74.5939	$74.59	$74.60	$74.60
Purchase #6	$173.65	12.669%	$195.6497	$195.65	$195.65	$195.60
Purchase #7	$23.38	8.784%	$25.4337	$25.43	$25.45	$25.40
7 purchase totals =	$1,072.31		$1,191.9686	$1,191.96	$1,192.00	$1,191.90