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	$67.72	13.868%	$77.1114	$77.11	$77.10	$77.10
Purchase #2	$52.36	13.523%	$59.4406	$59.44	$59.45	$59.40
Purchase #3	$71.73	8.294%	$77.6793	$77.68	$77.70	$77.70
Purchase #4	$96.72	6.858%	$103.3531	$103.35	$103.35	$103.40
Purchase #5	$127.98	13.435%	$145.1741	$145.17	$145.15	$145.20
Purchase #6	$37.36	9.152%	$40.7792	$40.78	$40.80	$40.80
Purchase #7	$121.33	3.835%	$125.983	$125.98	$126.00	$126.00
7 purchase totals =	$575.20		$629.5207	$629.51	$629.55	$629.60