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	$136.32	11.345%	$151.7855	$151.79	$151.80	$151.80
Purchase #2	$103.76	11.676%	$115.875	$115.88	$115.90	$115.90
Purchase #3	$234.30	10.269%	$258.3603	$258.36	$258.35	$258.40
Purchase #4	$76.89	11.195%	$85.4978	$85.50	$85.50	$85.50
Purchase #5	$99.27	12.344%	$111.5239	$111.52	$111.50	$111.50
Purchase #6	$32.97	5.841%	$34.8958	$34.90	$34.90	$34.90
Purchase #7	$30.84	7.196%	$33.0592	$33.06	$33.05	$33.10
7 purchase totals =	$714.35		$790.9975	$791.01	$791.00	$791.10