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	$89.33	11.440%	$99.5494	$99.55	$99.55	$99.50
Purchase #2	$49.79	7.673%	$53.6104	$53.61	$53.60	$53.60
Purchase #3	$205.83	5.441%	$217.0292	$217.03	$217.05	$217.00
Purchase #4	$50.59	11.568%	$56.4423	$56.44	$56.45	$56.40
Purchase #5	$168.54	5.213%	$177.326	$177.33	$177.35	$177.30
Purchase #6	$214.52	3.702%	$222.4615	$222.46	$222.45	$222.50
Purchase #7	$159.79	12.669%	$180.0338	$180.03	$180.05	$180.00
7 purchase totals =	$938.39		$1,006.4526	$1,006.45	$1,006.50	$1,006.30