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	$249.85	5.702%	$264.0964	$264.10	$264.10	$264.10
Purchase #2	$82.62	9.714%	$90.6457	$90.65	$90.65	$90.60
Purchase #3	$233.72	10.494%	$258.2466	$258.25	$258.25	$258.20
Purchase #4	$127.62	7.206%	$136.8163	$136.82	$136.80	$136.80
Purchase #5	$21.46	13.392%	$24.3339	$24.33	$24.35	$24.30
Purchase #6	$6.69	5.741%	$7.0741	$7.07	$7.05	$7.10
Purchase #7	$45.37	7.866%	$48.9388	$48.94	$48.95	$48.90
7 purchase totals =	$767.33		$830.1518	$830.16	$830.15	$830.00