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	$100.79	8.180%	$109.0346	$109.03	$109.05	$109.00
Purchase #2	$74.90	4.567%	$78.3207	$78.32	$78.30	$78.30
Purchase #3	$145.78	3.817%	$151.3444	$151.34	$151.35	$151.30
Purchase #4	$26.68	4.582%	$27.9025	$27.90	$27.90	$27.90
Purchase #5	$45.57	4.147%	$47.4598	$47.46	$47.45	$47.50
Purchase #6	$19.66	3.450%	$20.3383	$20.34	$20.35	$20.30
Purchase #7	$176.66	12.538%	$198.8096	$198.81	$198.80	$198.80
7 purchase totals =	$590.04		$633.2099	$633.20	$633.20	$633.10