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	$194.54	10.843%	$215.634	$215.63	$215.65	$215.60
Purchase #2	$101.70	7.443%	$109.2695	$109.27	$109.25	$109.30
Purchase #3	$59.39	9.489%	$65.0255	$65.03	$65.05	$65.00
Purchase #4	$45.41	9.527%	$49.7362	$49.74	$49.75	$49.70
Purchase #5	$176.26	6.848%	$188.3303	$188.33	$188.35	$188.30
Purchase #6	$90.85	10.669%	$100.5428	$100.54	$100.55	$100.50
Purchase #7	$249.34	5.315%	$262.5924	$262.59	$262.60	$262.60
7 purchase totals =	$917.49		$991.1307	$991.13	$991.20	$991.00