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	$179.47	5.795%	$189.8703	$189.87	$189.85	$189.90
Purchase #2	$242.91	13.423%	$275.5158	$275.52	$275.50	$275.50
Purchase #3	$86.89	4.303%	$90.6289	$90.63	$90.65	$90.60
Purchase #4	$245.63	6.455%	$261.4854	$261.49	$261.50	$261.50
Purchase #5	$196.36	10.362%	$216.7068	$216.71	$216.70	$216.70
Purchase #6	$178.63	3.184%	$184.3176	$184.32	$184.30	$184.30
Purchase #7	$31.54	9.251%	$34.4578	$34.46	$34.45	$34.50
7 purchase totals =	$1,161.43		$1,252.9826	$1,253.00	$1,252.95	$1,253.00