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	$104.43	11.581%	$116.524	$116.52	$116.50	$116.50
Purchase #2	$243.86	3.248%	$251.7806	$251.78	$251.80	$251.80
Purchase #3	$190.35	12.354%	$213.8658	$213.87	$213.85	$213.90
Purchase #4	$96.46	7.191%	$103.3964	$103.40	$103.40	$103.40
Purchase #5	$57.54	3.759%	$59.7029	$59.70	$59.70	$59.70
Purchase #6	$28.27	4.419%	$29.5193	$29.52	$29.50	$29.50
Purchase #7	$150.40	4.304%	$156.8732	$156.87	$156.85	$156.90
7 purchase totals =	$871.31		$931.6622	$931.66	$931.60	$931.70