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	$27.65	13.714%	$31.4419	$31.44	$31.45	$31.40
Purchase #2	$64.89	7.216%	$69.5725	$69.57	$69.55	$69.60
Purchase #3	$173.87	6.661%	$185.4515	$185.45	$185.45	$185.50
Purchase #4	$48.33	12.390%	$54.3181	$54.32	$54.30	$54.30
Purchase #5	$177.69	7.311%	$190.6809	$190.68	$190.70	$190.70
Purchase #6	$185.89	13.526%	$211.0335	$211.03	$211.05	$211.00
Purchase #7	$170.47	5.225%	$179.3771	$179.38	$179.40	$179.40
7 purchase totals =	$848.79		$921.8755	$921.87	$921.90	$921.90