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	$114.68	12.648%	$129.1847	$129.18	$129.20	$129.20
Purchase #2	$145.47	12.752%	$164.0203	$164.02	$164.00	$164.00
Purchase #3	$51.46	10.225%	$56.7218	$56.72	$56.70	$56.70
Purchase #4	$47.74	5.705%	$50.4636	$50.46	$50.45	$50.50
Purchase #5	$138.89	6.217%	$147.5248	$147.52	$147.50	$147.50
Purchase #6	$53.47	7.420%	$57.4375	$57.44	$57.45	$57.40
Purchase #7	$39.39	11.393%	$43.8777	$43.88	$43.90	$43.90
7 purchase totals =	$591.10		$649.2304	$649.22	$649.20	$649.20