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	$54.87	12.619%	$61.794	$61.79	$61.80	$61.80
Purchase #2	$218.26	13.321%	$247.3344	$247.33	$247.35	$247.30
Purchase #3	$108.90	8.712%	$118.3874	$118.39	$118.40	$118.40
Purchase #4	$182.73	7.529%	$196.4877	$196.49	$196.50	$196.50
Purchase #5	$50.41	9.451%	$55.1742	$55.17	$55.15	$55.20
Purchase #6	$20.32	5.223%	$21.3813	$21.38	$21.40	$21.40
Purchase #7	$46.81	5.237%	$49.2614	$49.26	$49.25	$49.30
7 purchase totals =	$682.30		$749.8204	$749.81	$749.85	$749.90