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	$206.93	8.320%	$224.1466	$224.15	$224.15	$224.10
Purchase #2	$196.79	10.557%	$217.5651	$217.57	$217.55	$217.60
Purchase #3	$99.83	9.221%	$109.0353	$109.04	$109.05	$109.00
Purchase #4	$59.42	3.172%	$61.3048	$61.30	$61.30	$61.30
Purchase #5	$122.44	12.719%	$138.0131	$138.01	$138.00	$138.00
Purchase #6	$192.25	12.513%	$216.3062	$216.31	$216.30	$216.30
Purchase #7	$10.58	12.323%	$11.8838	$11.88	$11.90	$11.90
7 purchase totals =	$888.24		$978.2549	$978.26	$978.25	$978.20