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	$137.65	8.855%	$149.8389	$149.84	$149.85	$149.80
Purchase #2	$104.59	3.542%	$108.2946	$108.29	$108.30	$108.30
Purchase #3	$80.25	12.288%	$90.1111	$90.11	$90.10	$90.10
Purchase #4	$99.76	12.111%	$111.8419	$111.84	$111.85	$111.80
Purchase #5	$15.42	10.662%	$17.0641	$17.06	$17.05	$17.10
Purchase #6	$162.29	12.804%	$183.0696	$183.07	$183.05	$183.10
Purchase #7	$38.42	3.247%	$39.6675	$39.67	$39.65	$39.70
7 purchase totals =	$638.38		$699.8877	$699.88	$699.85	$699.90