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	$80.44	12.339%	$90.3655	$90.37	$90.35	$90.40
Purchase #2	$158.39	9.377%	$173.2422	$173.24	$173.25	$173.20
Purchase #3	$85.96	5.194%	$90.4248	$90.42	$90.40	$90.40
Purchase #4	$183.57	12.575%	$206.6539	$206.65	$206.65	$206.70
Purchase #5	$188.92	12.331%	$212.2157	$212.22	$212.20	$212.20
Purchase #6	$211.42	13.807%	$240.6108	$240.61	$240.60	$240.60
Purchase #7	$31.98	6.628%	$34.0996	$34.10	$34.10	$34.10
7 purchase totals =	$940.68		$1,047.6125	$1,047.61	$1,047.55	$1,047.60