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	$142.41	13.224%	$161.2423	$161.24	$161.25	$161.20
Purchase #2	$159.25	6.406%	$169.4516	$169.45	$169.45	$169.50
Purchase #3	$156.37	12.372%	$175.7161	$175.72	$175.70	$175.70
Purchase #4	$166.71	3.367%	$172.3231	$172.32	$172.30	$172.30
Purchase #5	$225.72	9.386%	$246.9061	$246.91	$246.90	$246.90
Purchase #6	$144.45	6.457%	$153.7771	$153.78	$153.80	$153.80
Purchase #7	$19.68	7.568%	$21.1694	$21.17	$21.15	$21.20
7 purchase totals =	$1,014.59		$1,100.5857	$1,100.59	$1,100.55	$1,100.60