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	$106.87	13.297%	$121.0805	$121.08	$121.10	$121.10
Purchase #2	$164.67	10.173%	$181.4219	$181.42	$181.40	$181.40
Purchase #3	$93.38	10.731%	$103.4006	$103.40	$103.40	$103.40
Purchase #4	$128.38	3.175%	$132.4561	$132.46	$132.45	$132.50
Purchase #5	$69.44	11.668%	$77.5423	$77.54	$77.55	$77.50
Purchase #6	$61.65	11.695%	$68.86	$68.86	$68.85	$68.90
Purchase #7	$78.43	4.756%	$82.1601	$82.16	$82.15	$82.20
7 purchase totals =	$702.82		$766.9215	$766.92	$766.90	$767.00