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	$150.52	10.463%	$166.2689	$166.27	$166.25	$166.30
Purchase #2	$52.48	5.319%	$55.2714	$55.27	$55.25	$55.30
Purchase #3	$80.39	4.368%	$83.9014	$83.90	$83.90	$83.90
Purchase #4	$230.74	5.411%	$243.2253	$243.23	$243.25	$243.20
Purchase #5	$77.61	6.784%	$82.8751	$82.88	$82.90	$82.90
Purchase #6	$112.85	4.681%	$118.1325	$118.13	$118.15	$118.10
Purchase #7	$242.84	3.311%	$250.8804	$250.88	$250.90	$250.90
7 purchase totals =	$947.43		$1,000.5550	$1,000.56	$1,000.60	$1,000.60