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	$211.50	13.752%	$240.5855	$240.59	$240.60	$240.60
Purchase #2	$41.48	3.253%	$42.8293	$42.83	$42.85	$42.80
Purchase #3	$12.90	6.108%	$13.6879	$13.69	$13.70	$13.70
Purchase #4	$171.27	11.220%	$190.4865	$190.49	$190.50	$190.50
Purchase #5	$115.85	8.752%	$125.9892	$125.99	$126.00	$126.00
Purchase #6	$70.34	9.344%	$76.9126	$76.91	$76.90	$76.90
Purchase #7	$128.62	8.776%	$139.9077	$139.91	$139.90	$139.90
7 purchase totals =	$751.96		$830.3987	$830.41	$830.45	$830.40