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	$78.41	11.418%	$87.3629	$87.36	$87.35	$87.40
Purchase #2	$229.56	10.379%	$253.386	$253.39	$253.40	$253.40
Purchase #3	$44.38	5.376%	$46.7659	$46.77	$46.75	$46.80
Purchase #4	$245.55	12.349%	$275.873	$275.87	$275.85	$275.90
Purchase #5	$246.25	13.455%	$279.3829	$279.38	$279.40	$279.40
Purchase #6	$100.39	4.690%	$105.0983	$105.10	$105.10	$105.10
Purchase #7	$241.62	9.199%	$263.8466	$263.85	$263.85	$263.80
7 purchase totals =	$1,186.16		$1,311.7156	$1,311.72	$1,311.70	$1,311.80