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	$249.51	9.601%	$273.4655	$273.47	$273.45	$273.50
Purchase #2	$186.35	7.643%	$200.5927	$200.59	$200.60	$200.60
Purchase #3	$81.72	13.295%	$92.5847	$92.58	$92.60	$92.60
Purchase #4	$112.89	6.784%	$120.5485	$120.55	$120.55	$120.50
Purchase #5	$139.67	6.185%	$148.3086	$148.31	$148.30	$148.30
Purchase #6	$60.41	4.818%	$63.3206	$63.32	$63.30	$63.30
Purchase #7	$44.56	13.592%	$50.6166	$50.62	$50.60	$50.60
7 purchase totals =	$875.11		$949.4372	$949.44	$949.40	$949.40