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	$47.82	13.678%	$54.3608	$54.36	$54.35	$54.40
Purchase #2	$172.82	13.441%	$196.0487	$196.05	$196.05	$196.00
Purchase #3	$160.72	4.679%	$168.2401	$168.24	$168.25	$168.20
Purchase #4	$200.94	6.269%	$213.5369	$213.54	$213.55	$213.50
Purchase #5	$209.36	8.106%	$226.3307	$226.33	$226.35	$226.30
Purchase #6	$107.86	10.487%	$119.1713	$119.17	$119.15	$119.20
Purchase #7	$239.30	13.485%	$271.5696	$271.57	$271.55	$271.60
7 purchase totals =	$1,138.82		$1,249.2581	$1,249.26	$1,249.25	$1,249.20