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	$213.54	12.653%	$240.5592	$240.56	$240.55	$240.60
Purchase #2	$30.54	3.320%	$31.5539	$31.55	$31.55	$31.60
Purchase #3	$230.40	7.434%	$247.5279	$247.53	$247.55	$247.50
Purchase #4	$108.44	13.751%	$123.3516	$123.35	$123.35	$123.40
Purchase #5	$201.82	10.227%	$222.4601	$222.46	$222.45	$222.50
Purchase #6	$129.40	6.233%	$137.4655	$137.47	$137.45	$137.50
Purchase #7	$237.90	6.540%	$253.4587	$253.46	$253.45	$253.50
7 purchase totals =	$1,152.04		$1,256.3769	$1,256.38	$1,256.35	$1,256.60