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	$99.47	5.460%	$104.9011	$104.90	$104.90	$104.90
Purchase #2	$230.68	12.566%	$259.6672	$259.67	$259.65	$259.70
Purchase #3	$243.76	13.324%	$276.2386	$276.24	$276.25	$276.20
Purchase #4	$179.30	8.579%	$194.6821	$194.68	$194.70	$194.70
Purchase #5	$101.61	7.709%	$109.4431	$109.44	$109.45	$109.40
Purchase #6	$41.56	4.718%	$43.5208	$43.52	$43.50	$43.50
Purchase #7	$240.47	6.409%	$255.8817	$255.88	$255.90	$255.90
7 purchase totals =	$1,136.85		$1,244.3346	$1,244.33	$1,244.35	$1,244.30