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	$27.38	5.311%	$28.8342	$28.83	$28.85	$28.80
Purchase #2	$131.73	7.432%	$141.5202	$141.52	$141.50	$141.50
Purchase #3	$71.37	10.534%	$78.8881	$78.89	$78.90	$78.90
Purchase #4	$111.82	9.482%	$122.4228	$122.42	$122.40	$122.40
Purchase #5	$62.40	7.352%	$66.9876	$66.99	$67.00	$67.00
Purchase #6	$109.53	9.379%	$119.8028	$119.80	$119.80	$119.80
Purchase #7	$64.90	3.292%	$67.0365	$67.04	$67.05	$67.00
7 purchase totals =	$579.13		$625.4922	$625.49	$625.50	$625.40