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	$209.67	9.487%	$229.5614	$229.56	$229.55	$229.60
Purchase #2	$125.66	4.112%	$130.8271	$130.83	$130.85	$130.80
Purchase #3	$24.66	13.419%	$27.9691	$27.97	$27.95	$28.00
Purchase #4	$136.69	12.826%	$154.2219	$154.22	$154.20	$154.20
Purchase #5	$16.41	11.504%	$18.2978	$18.30	$18.30	$18.30
Purchase #6	$183.61	4.338%	$191.575	$191.58	$191.60	$191.60
Purchase #7	$211.33	6.753%	$225.6011	$225.60	$225.60	$225.60
7 purchase totals =	$908.03		$978.0534	$978.06	$978.05	$978.10