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	$48.32	10.480%	$53.3839	$53.38	$53.40	$53.40
Purchase #2	$84.88	10.625%	$93.8985	$93.90	$93.90	$93.90
Purchase #3	$34.82	12.796%	$39.2756	$39.28	$39.30	$39.30
Purchase #4	$167.42	5.398%	$176.4573	$176.46	$176.45	$176.50
Purchase #5	$133.56	8.322%	$144.6749	$144.67	$144.65	$144.70
Purchase #6	$209.51	9.222%	$228.831	$228.83	$228.85	$228.80
Purchase #7	$228.27	11.406%	$254.3065	$254.31	$254.30	$254.30
7 purchase totals =	$906.78		$990.8277	$990.83	$990.85	$990.90