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	$239.27	12.796%	$269.887	$269.89	$269.90	$269.90
Purchase #2	$196.97	3.762%	$204.38	$204.38	$204.40	$204.40
Purchase #3	$158.46	13.167%	$179.3244	$179.32	$179.30	$179.30
Purchase #4	$228.60	4.187%	$238.1715	$238.17	$238.15	$238.20
Purchase #5	$45.75	7.371%	$49.1222	$49.12	$49.10	$49.10
Purchase #6	$74.53	7.844%	$80.3761	$80.38	$80.40	$80.40
Purchase #7	$57.71	12.263%	$64.787	$64.79	$64.80	$64.80
7 purchase totals =	$1,001.29		$1,086.0482	$1,086.05	$1,086.05	$1,086.10