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	$17.89	9.137%	$19.5246	$19.52	$19.50	$19.50
Purchase #2	$225.48	6.561%	$240.2737	$240.27	$240.25	$240.30
Purchase #3	$150.65	7.178%	$161.4637	$161.46	$161.45	$161.50
Purchase #4	$65.48	4.350%	$68.3284	$68.33	$68.35	$68.30
Purchase #5	$35.66	3.446%	$36.8888	$36.89	$36.90	$36.90
Purchase #6	$136.74	4.151%	$142.4161	$142.42	$142.40	$142.40
Purchase #7	$33.27	13.701%	$37.8283	$37.83	$37.85	$37.80
7 purchase totals =	$665.17		$706.7236	$706.72	$706.70	$706.70