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	$103.74	3.574%	$107.4477	$107.45	$107.45	$107.40
Purchase #2	$203.68	10.819%	$225.7161	$225.72	$225.70	$225.70
Purchase #3	$191.62	12.508%	$215.5878	$215.59	$215.60	$215.60
Purchase #4	$59.95	9.120%	$65.4174	$65.42	$65.40	$65.40
Purchase #5	$27.81	5.244%	$29.2684	$29.27	$29.25	$29.30
Purchase #6	$57.25	7.589%	$61.5947	$61.59	$61.60	$61.60
Purchase #7	$116.39	12.749%	$131.2286	$131.23	$131.25	$131.20
7 purchase totals =	$760.44		$836.2607	$836.27	$836.25	$836.20