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	$77.73	3.421%	$80.3891	$80.39	$80.40	$80.40
Purchase #2	$185.92	5.711%	$196.5379	$196.54	$196.55	$196.50
Purchase #3	$186.98	4.254%	$194.9341	$194.93	$194.95	$194.90
Purchase #4	$138.52	11.161%	$153.9802	$153.98	$154.00	$154.00
Purchase #5	$219.56	13.795%	$249.8483	$249.85	$249.85	$249.80
Purchase #6	$84.65	5.799%	$89.5589	$89.56	$89.55	$89.60
Purchase #7	$93.62	12.476%	$105.3	$105.30	$105.30	$105.30
7 purchase totals =	$986.98		$1,070.5485	$1,070.55	$1,070.60	$1,070.50