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	$54.41	13.132%	$61.5551	$61.56	$61.55	$61.60
Purchase #2	$150.45	10.830%	$166.7437	$166.74	$166.75	$166.70
Purchase #3	$51.47	6.498%	$54.8145	$54.81	$54.80	$54.80
Purchase #4	$193.41	5.303%	$203.6665	$203.67	$203.65	$203.70
Purchase #5	$23.91	7.818%	$25.7793	$25.78	$25.80	$25.80
Purchase #6	$35.52	7.596%	$38.2181	$38.22	$38.20	$38.20
Purchase #7	$34.32	8.308%	$37.1713	$37.17	$37.15	$37.20
7 purchase totals =	$543.49		$587.9485	$587.95	$587.90	$588.00