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	$9.49	10.124%	$10.4508	$10.45	$10.45	$10.50
Purchase #2	$37.85	11.187%	$42.0843	$42.08	$42.10	$42.10
Purchase #3	$96.40	6.242%	$102.4173	$102.42	$102.40	$102.40
Purchase #4	$171.92	11.625%	$191.9057	$191.91	$191.90	$191.90
Purchase #5	$81.70	12.642%	$92.0285	$92.03	$92.05	$92.00
Purchase #6	$179.32	4.546%	$187.4719	$187.47	$187.45	$187.50
Purchase #7	$77.46	8.603%	$84.1239	$84.12	$84.10	$84.10
7 purchase totals =	$654.14		$710.4824	$710.48	$710.45	$710.50