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	$229.54	11.232%	$255.3219	$255.32	$255.30	$255.30
Purchase #2	$19.48	9.211%	$21.2743	$21.27	$21.25	$21.30
Purchase #3	$24.85	12.665%	$27.9973	$28.00	$28.00	$28.00
Purchase #4	$97.42	9.655%	$106.8259	$106.83	$106.85	$106.80
Purchase #5	$110.78	8.769%	$120.4943	$120.49	$120.50	$120.50
Purchase #6	$98.72	12.504%	$111.0639	$111.06	$111.05	$111.10
Purchase #7	$211.69	7.135%	$226.7941	$226.79	$226.80	$226.80
7 purchase totals =	$792.48		$869.7717	$869.76	$869.75	$869.80