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	$159.37	13.827%	$181.4061	$181.41	$181.40	$181.40
Purchase #2	$229.46	12.770%	$258.762	$258.76	$258.75	$258.80
Purchase #3	$19.44	12.785%	$21.9254	$21.93	$21.95	$21.90
Purchase #4	$103.43	3.153%	$106.6911	$106.69	$106.70	$106.70
Purchase #5	$185.89	5.824%	$196.7162	$196.72	$196.70	$196.70
Purchase #6	$40.87	11.537%	$45.5852	$45.59	$45.60	$45.60
Purchase #7	$98.89	10.591%	$109.3634	$109.36	$109.35	$109.40
7 purchase totals =	$837.35		$920.4494	$920.46	$920.45	$920.50