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	$132.77	13.186%	$150.2771	$150.28	$150.30	$150.30
Purchase #2	$80.62	8.403%	$87.3945	$87.39	$87.40	$87.40
Purchase #3	$195.70	13.723%	$222.5559	$222.56	$222.55	$222.60
Purchase #4	$50.30	9.617%	$55.1374	$55.14	$55.15	$55.10
Purchase #5	$138.62	7.444%	$148.9389	$148.94	$148.95	$148.90
Purchase #6	$52.97	13.476%	$60.1082	$60.11	$60.10	$60.10
Purchase #7	$78.59	9.302%	$85.9004	$85.90	$85.90	$85.90
7 purchase totals =	$729.57		$810.3124	$810.32	$810.35	$810.30