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	$146.40	13.682%	$166.4304	$166.43	$166.45	$166.40
Purchase #2	$245.53	10.438%	$271.1584	$271.16	$271.15	$271.20
Purchase #3	$142.81	3.256%	$147.4599	$147.46	$147.45	$147.50
Purchase #4	$109.89	4.546%	$114.8856	$114.89	$114.90	$114.90
Purchase #5	$127.77	9.679%	$140.1369	$140.14	$140.15	$140.10
Purchase #6	$186.76	12.668%	$210.4188	$210.42	$210.40	$210.40
Purchase #7	$116.95	7.818%	$126.0932	$126.09	$126.10	$126.10
7 purchase totals =	$1,076.11		$1,176.5832	$1,176.59	$1,176.60	$1,176.60