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	$24.98	12.604%	$28.1285	$28.13	$28.15	$28.10
Purchase #2	$227.72	13.126%	$257.6105	$257.61	$257.60	$257.60
Purchase #3	$173.31	11.300%	$192.894	$192.89	$192.90	$192.90
Purchase #4	$209.96	10.176%	$231.3255	$231.33	$231.35	$231.30
Purchase #5	$120.91	5.653%	$127.745	$127.75	$127.75	$127.70
Purchase #6	$179.45	12.516%	$201.91	$201.91	$201.90	$201.90
Purchase #7	$6.39	7.284%	$6.8554	$6.86	$6.85	$6.90
7 purchase totals =	$942.72		$1,046.4689	$1,046.48	$1,046.50	$1,046.40