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	$155.33	12.627%	$174.9435	$174.94	$174.95	$174.90
Purchase #2	$55.69	8.667%	$60.5167	$60.52	$60.50	$60.50
Purchase #3	$139.61	12.192%	$156.6313	$156.63	$156.65	$156.60
Purchase #4	$76.50	9.349%	$83.652	$83.65	$83.65	$83.70
Purchase #5	$127.61	8.128%	$137.9821	$137.98	$138.00	$138.00
Purchase #6	$159.86	10.351%	$176.4071	$176.41	$176.40	$176.40
Purchase #7	$86.85	3.130%	$89.5684	$89.57	$89.55	$89.60
7 purchase totals =	$801.45		$879.7011	$879.70	$879.70	$879.70