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	$25.41	6.417%	$27.0406	$27.04	$27.05	$27.00
Purchase #2	$148.87	13.717%	$169.2905	$169.29	$169.30	$169.30
Purchase #3	$92.38	13.103%	$104.4846	$104.48	$104.50	$104.50
Purchase #4	$79.72	7.532%	$85.7245	$85.72	$85.70	$85.70
Purchase #5	$103.54	9.504%	$113.3804	$113.38	$113.40	$113.40
Purchase #6	$235.87	13.145%	$266.8751	$266.88	$266.90	$266.90
Purchase #7	$143.98	9.616%	$157.8251	$157.83	$157.85	$157.80
7 purchase totals =	$829.77		$924.6208	$924.62	$924.70	$924.60