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	$204.51	13.536%	$232.1925	$232.19	$232.20	$232.20
Purchase #2	$105.86	8.811%	$115.1873	$115.19	$115.20	$115.20
Purchase #3	$152.55	7.615%	$164.1667	$164.17	$164.15	$164.20
Purchase #4	$81.54	9.530%	$89.3108	$89.31	$89.30	$89.30
Purchase #5	$101.94	7.491%	$109.5763	$109.58	$109.60	$109.60
Purchase #6	$234.55	7.392%	$251.8879	$251.89	$251.90	$251.90
Purchase #7	$142.60	12.833%	$160.8999	$160.90	$160.90	$160.90
7 purchase totals =	$1,023.55		$1,123.2214	$1,123.23	$1,123.25	$1,123.30