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	$166.93	13.679%	$189.7644	$189.76	$189.75	$189.80
Purchase #2	$99.42	4.126%	$103.5221	$103.52	$103.50	$103.50
Purchase #3	$92.63	5.571%	$97.7904	$97.79	$97.80	$97.80
Purchase #4	$157.61	11.328%	$175.4641	$175.46	$175.45	$175.50
Purchase #5	$37.67	11.445%	$41.9813	$41.98	$42.00	$42.00
Purchase #6	$168.79	5.364%	$177.8439	$177.84	$177.85	$177.80
Purchase #7	$190.58	3.294%	$196.8577	$196.86	$196.85	$196.90
7 purchase totals =	$913.63		$983.2239	$983.21	$983.20	$983.30