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	$110.87	11.192%	$123.2786	$123.28	$123.30	$123.30
Purchase #2	$84.95	5.480%	$89.6053	$89.61	$89.60	$89.60
Purchase #3	$82.32	8.313%	$89.1633	$89.16	$89.15	$89.20
Purchase #4	$199.51	3.696%	$206.8839	$206.88	$206.90	$206.90
Purchase #5	$217.74	12.440%	$244.8269	$244.83	$244.85	$244.80
Purchase #6	$186.26	11.333%	$207.3688	$207.37	$207.35	$207.40
Purchase #7	$136.73	3.857%	$142.0037	$142.00	$142.00	$142.00
7 purchase totals =	$1,018.38		$1,103.1305	$1,103.13	$1,103.15	$1,103.20