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	$167.90	10.223%	$185.0644	$185.06	$185.05	$185.10
Purchase #2	$148.76	12.278%	$167.0248	$167.02	$167.00	$167.00
Purchase #3	$221.88	4.300%	$231.4208	$231.42	$231.40	$231.40
Purchase #4	$37.30	8.515%	$40.4761	$40.48	$40.50	$40.50
Purchase #5	$52.30	5.316%	$55.0803	$55.08	$55.10	$55.10
Purchase #6	$23.49	12.286%	$26.376	$26.38	$26.40	$26.40
Purchase #7	$181.30	7.773%	$195.3924	$195.39	$195.40	$195.40
7 purchase totals =	$832.93		$900.8348	$900.83	$900.85	$900.90