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	$17.99	4.778%	$18.8496	$18.85	$18.85	$18.80
Purchase #2	$217.59	13.651%	$247.2932	$247.29	$247.30	$247.30
Purchase #3	$41.44	5.151%	$43.5746	$43.57	$43.55	$43.60
Purchase #4	$85.40	4.423%	$89.1772	$89.18	$89.20	$89.20
Purchase #5	$84.83	5.498%	$89.494	$89.49	$89.50	$89.50
Purchase #6	$234.73	6.136%	$249.133	$249.13	$249.15	$249.10
Purchase #7	$173.32	9.226%	$189.3105	$189.31	$189.30	$189.30
7 purchase totals =	$855.30		$926.8321	$926.82	$926.85	$926.80