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	$89.55	12.193%	$100.4688	$100.47	$100.45	$100.50
Purchase #2	$127.90	12.871%	$144.362	$144.36	$144.35	$144.40
Purchase #3	$129.84	7.524%	$139.6092	$139.61	$139.60	$139.60
Purchase #4	$56.43	5.749%	$59.6742	$59.67	$59.65	$59.70
Purchase #5	$49.77	11.120%	$55.3044	$55.30	$55.30	$55.30
Purchase #6	$120.75	9.754%	$132.528	$132.53	$132.55	$132.50
Purchase #7	$69.59	8.135%	$75.2511	$75.25	$75.25	$75.30
7 purchase totals =	$643.83		$707.1977	$707.19	$707.15	$707.30