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	$39.90	7.165%	$42.7588	$42.76	$42.75	$42.80
Purchase #2	$203.73	8.780%	$221.6175	$221.62	$221.60	$221.60
Purchase #3	$116.59	11.106%	$129.5385	$129.54	$129.55	$129.50
Purchase #4	$90.41	11.379%	$100.6978	$100.70	$100.70	$100.70
Purchase #5	$183.51	11.640%	$204.8706	$204.87	$204.85	$204.90
Purchase #6	$132.27	7.243%	$141.8503	$141.85	$141.85	$141.90
Purchase #7	$154.93	3.418%	$160.2255	$160.23	$160.25	$160.20
7 purchase totals =	$921.34		$1,001.5590	$1,001.57	$1,001.55	$1,001.60