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	$75.40	9.665%	$82.6874	$82.69	$82.70	$82.70
Purchase #2	$159.78	11.809%	$178.6484	$178.65	$178.65	$178.60
Purchase #3	$63.50	6.592%	$67.6859	$67.69	$67.70	$67.70
Purchase #4	$121.68	6.824%	$129.9834	$129.98	$130.00	$130.00
Purchase #5	$133.27	10.224%	$146.8955	$146.90	$146.90	$146.90
Purchase #6	$19.27	13.652%	$21.9007	$21.90	$21.90	$21.90
Purchase #7	$173.69	3.699%	$180.1148	$180.11	$180.10	$180.10
7 purchase totals =	$746.59		$807.9161	$807.92	$807.95	$807.90