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	$109.30	8.330%	$118.4047	$118.40	$118.40	$118.40
Purchase #2	$132.33	3.210%	$136.5778	$136.58	$136.60	$136.60
Purchase #3	$97.82	3.729%	$101.4677	$101.47	$101.45	$101.50
Purchase #4	$66.69	5.608%	$70.43	$70.43	$70.45	$70.40
Purchase #5	$135.82	6.380%	$144.4853	$144.49	$144.50	$144.50
Purchase #6	$32.34	13.592%	$36.7357	$36.74	$36.75	$36.70
Purchase #7	$28.70	12.676%	$32.338	$32.34	$32.35	$32.30
7 purchase totals =	$603.00		$640.4392	$640.45	$640.50	$640.40