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	$100.56	9.751%	$110.3656	$110.37	$110.35	$110.40
Purchase #2	$159.27	5.111%	$167.4103	$167.41	$167.40	$167.40
Purchase #3	$189.91	4.616%	$198.6762	$198.68	$198.70	$198.70
Purchase #4	$53.69	10.460%	$59.306	$59.31	$59.30	$59.30
Purchase #5	$40.36	13.105%	$45.6492	$45.65	$45.65	$45.60
Purchase #6	$135.41	5.483%	$142.8345	$142.83	$142.85	$142.80
Purchase #7	$76.99	12.253%	$86.4236	$86.42	$86.40	$86.40
7 purchase totals =	$756.19		$810.6654	$810.67	$810.65	$810.60