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	$156.51	7.486%	$168.2263	$168.23	$168.25	$168.20
Purchase #2	$246.66	6.391%	$262.424	$262.42	$262.40	$262.40
Purchase #3	$114.85	3.755%	$119.1626	$119.16	$119.15	$119.20
Purchase #4	$53.42	11.110%	$59.355	$59.36	$59.35	$59.40
Purchase #5	$126.35	13.389%	$143.267	$143.27	$143.25	$143.30
Purchase #6	$92.57	13.628%	$105.1854	$105.19	$105.20	$105.20
Purchase #7	$210.75	10.782%	$233.4731	$233.47	$233.45	$233.50
7 purchase totals =	$1,001.11		$1,091.0934	$1,091.10	$1,091.05	$1,091.20