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	$103.56	5.690%	$109.4526	$109.45	$109.45	$109.50
Purchase #2	$62.88	7.290%	$67.464	$67.46	$67.45	$67.50
Purchase #3	$11.56	5.370%	$12.1808	$12.18	$12.20	$12.20
Purchase #4	$99.85	13.430%	$113.2599	$113.26	$113.25	$113.30
Purchase #5	$81.36	9.405%	$89.0119	$89.01	$89.00	$89.00
Purchase #6	$16.81	3.254%	$17.357	$17.36	$17.35	$17.40
Purchase #7	$129.85	8.142%	$140.4224	$140.42	$140.40	$140.40
7 purchase totals =	$505.87		$549.1486	$549.14	$549.10	$549.30