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	$19.55	11.810%	$21.8589	$21.86	$21.85	$21.90
Purchase #2	$230.52	8.486%	$250.0819	$250.08	$250.10	$250.10
Purchase #3	$47.41	11.820%	$53.0139	$53.01	$53.00	$53.00
Purchase #4	$56.88	6.264%	$60.443	$60.44	$60.45	$60.40
Purchase #5	$88.58	12.722%	$99.8491	$99.85	$99.85	$99.80
Purchase #6	$182.47	8.268%	$197.5566	$197.56	$197.55	$197.60
Purchase #7	$89.61	10.569%	$99.0809	$99.08	$99.10	$99.10
7 purchase totals =	$715.02		$781.8843	$781.88	$781.90	$781.90