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	$105.73	6.611%	$112.7198	$112.72	$112.70	$112.70
Purchase #2	$236.77	12.774%	$267.015	$267.02	$267.00	$267.00
Purchase #3	$17.40	7.196%	$18.6521	$18.65	$18.65	$18.70
Purchase #4	$10.85	6.839%	$11.592	$11.59	$11.60	$11.60
Purchase #5	$156.83	4.645%	$164.1148	$164.11	$164.10	$164.10
Purchase #6	$55.49	6.205%	$58.9332	$58.93	$58.95	$58.90
Purchase #7	$95.33	10.661%	$105.4931	$105.49	$105.50	$105.50
7 purchase totals =	$678.40		$738.5200	$738.51	$738.50	$738.50