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	$231.49	9.578%	$253.6621	$253.66	$253.65	$253.70
Purchase #2	$37.72	4.268%	$39.3299	$39.33	$39.35	$39.30
Purchase #3	$234.67	12.758%	$264.6092	$264.61	$264.60	$264.60
Purchase #4	$156.72	7.213%	$168.0242	$168.02	$168.00	$168.00
Purchase #5	$21.76	11.453%	$24.2522	$24.25	$24.25	$24.30
Purchase #6	$102.63	4.150%	$106.8891	$106.89	$106.90	$106.90
Purchase #7	$18.81	13.762%	$21.3986	$21.40	$21.40	$21.40
7 purchase totals =	$803.80		$878.1653	$878.16	$878.15	$878.20