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	$76.48	3.119%	$78.8654	$78.87	$78.85	$78.90
Purchase #2	$157.60	13.574%	$178.9926	$178.99	$179.00	$179.00
Purchase #3	$57.92	3.294%	$59.8279	$59.83	$59.85	$59.80
Purchase #4	$201.81	13.733%	$229.5246	$229.52	$229.50	$229.50
Purchase #5	$123.74	12.554%	$139.2743	$139.27	$139.25	$139.30
Purchase #6	$203.25	10.110%	$223.7986	$223.80	$223.80	$223.80
Purchase #7	$150.98	4.419%	$157.6518	$157.65	$157.65	$157.70
7 purchase totals =	$971.78		$1,067.9352	$1,067.93	$1,067.90	$1,068.00