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	$73.62	12.503%	$82.8247	$82.82	$82.80	$82.80
Purchase #2	$88.59	6.574%	$94.4139	$94.41	$94.40	$94.40
Purchase #3	$18.33	11.556%	$20.4482	$20.45	$20.45	$20.40
Purchase #4	$175.43	5.839%	$185.6734	$185.67	$185.65	$185.70
Purchase #5	$176.85	3.450%	$182.9513	$182.95	$182.95	$183.00
Purchase #6	$74.72	12.338%	$83.939	$83.94	$83.95	$83.90
Purchase #7	$63.34	8.712%	$68.8582	$68.86	$68.85	$68.90
7 purchase totals =	$670.88		$719.1087	$719.10	$719.05	$719.10