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	$109.90	12.286%	$123.4023	$123.40	$123.40	$123.40
Purchase #2	$59.97	12.840%	$67.6701	$67.67	$67.65	$67.70
Purchase #3	$63.30	11.558%	$70.6162	$70.62	$70.60	$70.60
Purchase #4	$53.82	6.490%	$57.3129	$57.31	$57.30	$57.30
Purchase #5	$186.79	9.151%	$203.8832	$203.88	$203.90	$203.90
Purchase #6	$119.29	12.275%	$133.9328	$133.93	$133.95	$133.90
Purchase #7	$80.84	11.722%	$90.3161	$90.32	$90.30	$90.30
7 purchase totals =	$673.91		$747.1336	$747.13	$747.10	$747.10