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	$221.66	12.768%	$249.9615	$249.96	$249.95	$250.00
Purchase #2	$50.89	5.852%	$53.8681	$53.87	$53.85	$53.90
Purchase #3	$127.73	10.253%	$140.8262	$140.83	$140.85	$140.80
Purchase #4	$79.78	12.104%	$89.4366	$89.44	$89.45	$89.40
Purchase #5	$52.27	3.753%	$54.2317	$54.23	$54.25	$54.20
Purchase #6	$160.83	6.210%	$170.8175	$170.82	$170.80	$170.80
Purchase #7	$167.82	13.193%	$189.9605	$189.96	$189.95	$190.00
7 purchase totals =	$860.98		$949.1021	$949.11	$949.10	$949.10