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	$13.73	11.792%	$15.349	$15.35	$15.35	$15.30
Purchase #2	$175.73	8.783%	$191.1644	$191.16	$191.15	$191.20
Purchase #3	$230.87	8.612%	$250.7525	$250.75	$250.75	$250.80
Purchase #4	$191.37	3.839%	$198.7167	$198.72	$198.70	$198.70
Purchase #5	$45.36	5.322%	$47.7741	$47.77	$47.75	$47.80
Purchase #6	$239.93	4.560%	$250.8708	$250.87	$250.85	$250.90
Purchase #7	$234.75	3.152%	$242.1493	$242.15	$242.15	$242.10
7 purchase totals =	$1,131.74		$1,196.7768	$1,196.77	$1,196.70	$1,196.80