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	$129.72	12.203%	$145.5497	$145.55	$145.55	$145.50
Purchase #2	$198.31	12.490%	$223.0789	$223.08	$223.10	$223.10
Purchase #3	$112.53	9.590%	$123.3216	$123.32	$123.30	$123.30
Purchase #4	$81.77	4.745%	$85.65	$85.65	$85.65	$85.70
Purchase #5	$56.92	11.744%	$63.6047	$63.60	$63.60	$63.60
Purchase #6	$39.74	4.800%	$41.6475	$41.65	$41.65	$41.60
Purchase #7	$125.48	11.791%	$140.2753	$140.28	$140.30	$140.30
7 purchase totals =	$744.47		$823.1277	$823.13	$823.15	$823.10