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	$241.62	3.262%	$249.5016	$249.50	$249.50	$249.50
Purchase #2	$210.70	13.194%	$238.4998	$238.50	$238.50	$238.50
Purchase #3	$104.56	13.304%	$118.4707	$118.47	$118.45	$118.50
Purchase #4	$234.66	12.674%	$264.4008	$264.40	$264.40	$264.40
Purchase #5	$97.54	13.600%	$110.8054	$110.81	$110.80	$110.80
Purchase #6	$102.94	12.739%	$116.0535	$116.05	$116.05	$116.10
Purchase #7	$112.34	9.799%	$123.3482	$123.35	$123.35	$123.30
7 purchase totals =	$1,104.36		$1,221.0800	$1,221.08	$1,221.05	$1,221.10