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	$169.27	5.187%	$178.05	$178.05	$178.05	$178.10
Purchase #2	$92.33	13.809%	$105.0798	$105.08	$105.10	$105.10
Purchase #3	$44.69	11.732%	$49.933	$49.93	$49.95	$49.90
Purchase #4	$221.71	6.196%	$235.4472	$235.45	$235.45	$235.40
Purchase #5	$150.33	12.129%	$168.5635	$168.56	$168.55	$168.60
Purchase #6	$151.97	3.163%	$156.7768	$156.78	$156.80	$156.80
Purchase #7	$250.95	11.310%	$279.3324	$279.33	$279.35	$279.30
7 purchase totals =	$1,081.25		$1,173.1827	$1,173.18	$1,173.25	$1,173.20