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	$33.65	12.617%	$37.8956	$37.90	$37.90	$37.90
Purchase #2	$172.98	5.439%	$182.3884	$182.39	$182.40	$182.40
Purchase #3	$163.65	13.274%	$185.3729	$185.37	$185.35	$185.40
Purchase #4	$203.65	5.349%	$214.5432	$214.54	$214.55	$214.50
Purchase #5	$204.83	13.172%	$231.8102	$231.81	$231.80	$231.80
Purchase #6	$179.76	3.185%	$185.4854	$185.49	$185.50	$185.50
Purchase #7	$150.49	13.235%	$170.4074	$170.41	$170.40	$170.40
7 purchase totals =	$1,109.01		$1,207.9031	$1,207.91	$1,207.90	$1,207.90