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	$192.96	11.596%	$215.3356	$215.34	$215.35	$215.30
Purchase #2	$158.83	11.607%	$177.2654	$177.27	$177.25	$177.30
Purchase #3	$197.85	12.470%	$222.5219	$222.52	$222.50	$222.50
Purchase #4	$77.52	9.716%	$85.0518	$85.05	$85.05	$85.10
Purchase #5	$18.64	9.706%	$20.4492	$20.45	$20.45	$20.40
Purchase #6	$83.52	12.378%	$93.8581	$93.86	$93.85	$93.90
Purchase #7	$68.61	6.190%	$72.857	$72.86	$72.85	$72.90
7 purchase totals =	$797.93		$887.3390	$887.35	$887.30	$887.40