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	$223.76	11.642%	$249.8101	$249.81	$249.80	$249.80
Purchase #2	$19.26	11.799%	$21.5325	$21.53	$21.55	$21.50
Purchase #3	$186.75	5.298%	$196.644	$196.64	$196.65	$196.60
Purchase #4	$167.43	5.613%	$176.8278	$176.83	$176.85	$176.80
Purchase #5	$41.40	11.221%	$46.0455	$46.05	$46.05	$46.00
Purchase #6	$142.44	4.110%	$148.2943	$148.29	$148.30	$148.30
Purchase #7	$228.59	9.676%	$250.7084	$250.71	$250.70	$250.70
7 purchase totals =	$1,009.63		$1,089.8626	$1,089.86	$1,089.90	$1,089.70