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	$103.59	5.714%	$109.5091	$109.51	$109.50	$109.50
Purchase #2	$151.44	3.479%	$156.7086	$156.71	$156.70	$156.70
Purchase #3	$229.33	8.734%	$249.3597	$249.36	$249.35	$249.40
Purchase #4	$213.59	10.150%	$235.2694	$235.27	$235.25	$235.30
Purchase #5	$6.89	10.302%	$7.5998	$7.60	$7.60	$7.60
Purchase #6	$49.32	7.419%	$52.9791	$52.98	$53.00	$53.00
Purchase #7	$152.26	9.709%	$167.0429	$167.04	$167.05	$167.00
7 purchase totals =	$906.42		$978.4686	$978.47	$978.45	$978.50