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	$48.27	6.865%	$51.5837	$51.58	$51.60	$51.60
Purchase #2	$49.85	12.440%	$56.0513	$56.05	$56.05	$56.10
Purchase #3	$127.72	7.774%	$137.649	$137.65	$137.65	$137.60
Purchase #4	$189.87	3.659%	$196.8173	$196.82	$196.80	$196.80
Purchase #5	$179.84	9.327%	$196.6137	$196.61	$196.60	$196.60
Purchase #6	$37.98	6.413%	$40.4157	$40.42	$40.40	$40.40
Purchase #7	$124.60	8.535%	$135.2346	$135.23	$135.25	$135.20
7 purchase totals =	$758.13		$814.3653	$814.36	$814.35	$814.30