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	$30.25	4.281%	$31.545	$31.55	$31.55	$31.50
Purchase #2	$184.66	6.285%	$196.2659	$196.27	$196.25	$196.30
Purchase #3	$117.67	4.719%	$123.2228	$123.22	$123.20	$123.20
Purchase #4	$74.51	11.756%	$83.2694	$83.27	$83.25	$83.30
Purchase #5	$92.98	11.255%	$103.4449	$103.44	$103.45	$103.40
Purchase #6	$141.37	8.871%	$153.9109	$153.91	$153.90	$153.90
Purchase #7	$117.76	11.608%	$131.4296	$131.43	$131.45	$131.40
7 purchase totals =	$759.20		$823.0885	$823.09	$823.05	$823.00