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	$53.85	4.375%	$56.2059	$56.21	$56.20	$56.20
Purchase #2	$186.90	7.248%	$200.4465	$200.45	$200.45	$200.40
Purchase #3	$36.71	9.149%	$40.0686	$40.07	$40.05	$40.10
Purchase #4	$39.74	10.542%	$43.9294	$43.93	$43.95	$43.90
Purchase #5	$138.39	9.860%	$152.0353	$152.04	$152.05	$152.00
Purchase #6	$229.29	12.208%	$257.2817	$257.28	$257.30	$257.30
Purchase #7	$9.51	12.592%	$10.7075	$10.71	$10.70	$10.70
7 purchase totals =	$694.39		$760.6749	$760.69	$760.70	$760.60