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	$249.78	7.539%	$268.6109	$268.61	$268.60	$268.60
Purchase #2	$155.68	6.139%	$165.2372	$165.24	$165.25	$165.20
Purchase #3	$140.60	4.469%	$146.8834	$146.88	$146.90	$146.90
Purchase #4	$198.56	12.253%	$222.8896	$222.89	$222.90	$222.90
Purchase #5	$97.52	4.179%	$101.5954	$101.60	$101.60	$101.60
Purchase #6	$102.58	13.552%	$116.4816	$116.48	$116.50	$116.50
Purchase #7	$178.84	5.172%	$188.0896	$188.09	$188.10	$188.10
7 purchase totals =	$1,123.56		$1,209.7877	$1,209.79	$1,209.85	$1,209.80