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	$75.47	9.703%	$82.7929	$82.79	$82.80	$82.80
Purchase #2	$54.53	10.632%	$60.3276	$60.33	$60.35	$60.30
Purchase #3	$231.82	11.807%	$259.191	$259.19	$259.20	$259.20
Purchase #4	$237.60	5.421%	$250.4803	$250.48	$250.50	$250.50
Purchase #5	$11.68	6.150%	$12.3983	$12.40	$12.40	$12.40
Purchase #6	$52.54	13.302%	$59.5289	$59.53	$59.55	$59.50
Purchase #7	$155.52	3.764%	$161.3738	$161.37	$161.35	$161.40
7 purchase totals =	$819.16		$886.0928	$886.09	$886.15	$886.10