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	$137.59	5.874%	$145.672	$145.67	$145.65	$145.70
Purchase #2	$207.59	12.488%	$233.5138	$233.51	$233.50	$233.50
Purchase #3	$249.88	13.225%	$282.9266	$282.93	$282.95	$282.90
Purchase #4	$216.69	13.215%	$245.3256	$245.33	$245.35	$245.30
Purchase #5	$129.37	5.461%	$136.4349	$136.43	$136.45	$136.40
Purchase #6	$103.73	5.551%	$109.4881	$109.49	$109.50	$109.50
Purchase #7	$99.62	13.744%	$113.3118	$113.31	$113.30	$113.30
7 purchase totals =	$1,144.47		$1,266.6728	$1,266.67	$1,266.70	$1,266.60