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	$104.50	13.773%	$118.8928	$118.89	$118.90	$118.90
Purchase #2	$12.31	6.446%	$13.1035	$13.10	$13.10	$13.10
Purchase #3	$72.28	13.634%	$82.1347	$82.13	$82.15	$82.10
Purchase #4	$244.77	10.692%	$270.9408	$270.94	$270.95	$270.90
Purchase #5	$47.48	8.245%	$51.3947	$51.39	$51.40	$51.40
Purchase #6	$229.31	8.230%	$248.1822	$248.18	$248.20	$248.20
Purchase #7	$40.86	10.128%	$44.9983	$45.00	$45.00	$45.00
7 purchase totals =	$751.51		$829.6470	$829.63	$829.70	$829.60