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	$36.65	12.234%	$41.1338	$41.13	$41.15	$41.10
Purchase #2	$65.33	8.511%	$70.8902	$70.89	$70.90	$70.90
Purchase #3	$222.77	8.425%	$241.5384	$241.54	$241.55	$241.50
Purchase #4	$181.56	9.218%	$198.2962	$198.30	$198.30	$198.30
Purchase #5	$68.86	5.120%	$72.3856	$72.39	$72.40	$72.40
Purchase #6	$178.59	6.251%	$189.7537	$189.75	$189.75	$189.80
Purchase #7	$34.80	13.687%	$39.5631	$39.56	$39.55	$39.60
7 purchase totals =	$788.56		$853.5610	$853.56	$853.60	$853.60