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	$49.46	12.280%	$55.5337	$55.53	$55.55	$55.50
Purchase #2	$194.66	6.592%	$207.492	$207.49	$207.50	$207.50
Purchase #3	$59.58	9.296%	$65.1186	$65.12	$65.10	$65.10
Purchase #4	$196.83	10.139%	$216.7866	$216.79	$216.80	$216.80
Purchase #5	$13.33	8.228%	$14.4268	$14.43	$14.45	$14.40
Purchase #6	$177.43	10.710%	$196.4328	$196.43	$196.45	$196.40
Purchase #7	$63.95	10.153%	$70.4428	$70.44	$70.45	$70.40
7 purchase totals =	$755.24		$826.2333	$826.23	$826.30	$826.10