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	$249.34	4.652%	$260.9393	$260.94	$260.95	$260.90
Purchase #2	$99.64	7.673%	$107.2854	$107.29	$107.30	$107.30
Purchase #3	$39.56	6.482%	$42.1243	$42.12	$42.10	$42.10
Purchase #4	$15.29	3.354%	$15.8028	$15.80	$15.80	$15.80
Purchase #5	$85.73	4.778%	$89.8262	$89.83	$89.85	$89.80
Purchase #6	$63.29	13.343%	$71.7348	$71.73	$71.75	$71.70
Purchase #7	$92.47	13.137%	$104.6178	$104.62	$104.60	$104.60
7 purchase totals =	$645.32		$692.3306	$692.33	$692.35	$692.20