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	$237.53	12.543%	$267.3234	$267.32	$267.30	$267.30
Purchase #2	$237.66	13.854%	$270.5854	$270.59	$270.60	$270.60
Purchase #3	$85.38	5.759%	$90.297	$90.30	$90.30	$90.30
Purchase #4	$179.28	11.678%	$200.2163	$200.22	$200.20	$200.20
Purchase #5	$103.83	4.553%	$108.5574	$108.56	$108.55	$108.60
Purchase #6	$53.32	5.730%	$56.3752	$56.38	$56.40	$56.40
Purchase #7	$214.34	9.656%	$235.0367	$235.04	$235.05	$235.00
7 purchase totals =	$1,111.34		$1,228.3914	$1,228.41	$1,228.40	$1,228.40