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	$156.56	3.134%	$161.4666	$161.47	$161.45	$161.50
Purchase #2	$63.59	5.825%	$67.2941	$67.29	$67.30	$67.30
Purchase #3	$237.78	6.455%	$253.1287	$253.13	$253.15	$253.10
Purchase #4	$166.30	11.192%	$184.9123	$184.91	$184.90	$184.90
Purchase #5	$90.89	8.571%	$98.6802	$98.68	$98.70	$98.70
Purchase #6	$92.32	12.142%	$103.5295	$103.53	$103.55	$103.50
Purchase #7	$106.70	10.772%	$118.1937	$118.19	$118.20	$118.20
7 purchase totals =	$914.14		$987.2051	$987.20	$987.25	$987.20