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	$49.91	11.716%	$55.7575	$55.76	$55.75	$55.80
Purchase #2	$82.32	3.592%	$85.2769	$85.28	$85.30	$85.30
Purchase #3	$99.87	13.252%	$113.1048	$113.10	$113.10	$113.10
Purchase #4	$83.76	10.772%	$92.7826	$92.78	$92.80	$92.80
Purchase #5	$52.72	3.409%	$54.5172	$54.52	$54.50	$54.50
Purchase #6	$98.94	9.843%	$108.6787	$108.68	$108.70	$108.70
Purchase #7	$72.48	13.606%	$82.3416	$82.34	$82.35	$82.30
7 purchase totals =	$540.00		$592.4593	$592.46	$592.50	$592.50