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	$146.59	8.751%	$159.4181	$159.42	$159.40	$159.40
Purchase #2	$19.71	3.442%	$20.3884	$20.39	$20.40	$20.40
Purchase #3	$125.85	13.274%	$142.5553	$142.56	$142.55	$142.60
Purchase #4	$157.30	6.758%	$167.9303	$167.93	$167.95	$167.90
Purchase #5	$145.92	4.419%	$152.3682	$152.37	$152.35	$152.40
Purchase #6	$116.33	6.106%	$123.4331	$123.43	$123.45	$123.40
Purchase #7	$218.60	5.186%	$229.9366	$229.94	$229.95	$229.90
7 purchase totals =	$930.30		$996.0300	$996.04	$996.05	$996.00