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	$146.64	12.293%	$164.6665	$164.67	$164.65	$164.70
Purchase #2	$225.40	12.119%	$252.7162	$252.72	$252.70	$252.70
Purchase #3	$73.47	7.374%	$78.8877	$78.89	$78.90	$78.90
Purchase #4	$70.93	10.722%	$78.5351	$78.54	$78.55	$78.50
Purchase #5	$74.93	3.430%	$77.5001	$77.50	$77.50	$77.50
Purchase #6	$168.72	10.510%	$186.4525	$186.45	$186.45	$186.50
Purchase #7	$233.99	11.704%	$261.3762	$261.38	$261.40	$261.40
7 purchase totals =	$994.08		$1,100.1343	$1,100.15	$1,100.15	$1,100.20