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	$30.85	5.268%	$32.4752	$32.48	$32.50	$32.50
Purchase #2	$71.62	11.507%	$79.8613	$79.86	$79.85	$79.90
Purchase #3	$106.86	10.347%	$117.9168	$117.92	$117.90	$117.90
Purchase #4	$14.40	10.113%	$15.8563	$15.86	$15.85	$15.90
Purchase #5	$240.49	3.874%	$249.8066	$249.81	$249.80	$249.80
Purchase #6	$95.37	10.654%	$105.5307	$105.53	$105.55	$105.50
Purchase #7	$138.93	8.183%	$150.2986	$150.30	$150.30	$150.30
7 purchase totals =	$698.52		$751.7455	$751.76	$751.75	$751.80