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	$99.37	10.300%	$109.6051	$109.61	$109.60	$109.60
Purchase #2	$206.73	5.584%	$218.2738	$218.27	$218.25	$218.30
Purchase #3	$103.43	10.542%	$114.3336	$114.33	$114.35	$114.30
Purchase #4	$67.87	9.352%	$74.2172	$74.22	$74.20	$74.20
Purchase #5	$10.79	8.609%	$11.7189	$11.72	$11.70	$11.70
Purchase #6	$183.32	7.215%	$196.5465	$196.55	$196.55	$196.50
Purchase #7	$67.49	5.225%	$71.0164	$71.02	$71.00	$71.00
7 purchase totals =	$739.00		$795.7115	$795.72	$795.65	$795.60