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	$103.76	9.174%	$113.2789	$113.28	$113.30	$113.30
Purchase #2	$79.81	12.768%	$90.0001	$90.00	$90.00	$90.00
Purchase #3	$186.94	13.259%	$211.7264	$211.73	$211.75	$211.70
Purchase #4	$223.91	9.842%	$245.9472	$245.95	$245.95	$245.90
Purchase #5	$35.70	13.523%	$40.5277	$40.53	$40.55	$40.50
Purchase #6	$231.78	8.115%	$250.5889	$250.59	$250.60	$250.60
Purchase #7	$28.56	4.688%	$29.8989	$29.90	$29.90	$29.90
7 purchase totals =	$890.46		$981.9681	$981.98	$982.05	$981.90