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	$15.41	7.314%	$16.5371	$16.54	$16.55	$16.50
Purchase #2	$137.70	11.261%	$153.2064	$153.21	$153.20	$153.20
Purchase #3	$103.99	4.631%	$108.8058	$108.81	$108.80	$108.80
Purchase #4	$25.37	11.335%	$28.2457	$28.25	$28.25	$28.20
Purchase #5	$198.50	11.595%	$221.5161	$221.52	$221.50	$221.50
Purchase #6	$94.64	6.207%	$100.5143	$100.51	$100.50	$100.50
Purchase #7	$215.79	3.196%	$222.6866	$222.69	$222.70	$222.70
7 purchase totals =	$791.40		$851.5120	$851.53	$851.50	$851.40