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	$54.90	11.752%	$61.3518	$61.35	$61.35	$61.40
Purchase #2	$154.54	12.478%	$173.8235	$173.82	$173.80	$173.80
Purchase #3	$127.77	3.675%	$132.4655	$132.47	$132.45	$132.50
Purchase #4	$41.48	4.704%	$43.4312	$43.43	$43.45	$43.40
Purchase #5	$164.67	13.672%	$187.1837	$187.18	$187.20	$187.20
Purchase #6	$128.95	4.583%	$134.8598	$134.86	$134.85	$134.90
Purchase #7	$99.28	11.427%	$110.6247	$110.62	$110.60	$110.60
7 purchase totals =	$771.59		$843.7402	$843.73	$843.70	$843.80