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	$223.88	12.732%	$252.3844	$252.38	$252.40	$252.40
Purchase #2	$59.87	6.756%	$63.9148	$63.91	$63.90	$63.90
Purchase #3	$160.33	13.449%	$181.8928	$181.89	$181.90	$181.90
Purchase #4	$172.54	3.414%	$178.4305	$178.43	$178.45	$178.40
Purchase #5	$193.60	3.515%	$200.405	$200.41	$200.40	$200.40
Purchase #6	$85.41	4.413%	$89.1791	$89.18	$89.20	$89.20
Purchase #7	$6.66	8.664%	$7.237	$7.24	$7.25	$7.20
7 purchase totals =	$902.29		$973.4436	$973.44	$973.50	$973.40