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	$129.44	9.627%	$141.9012	$141.90	$141.90	$141.90
Purchase #2	$244.72	13.857%	$278.6309	$278.63	$278.65	$278.60
Purchase #3	$27.98	6.576%	$29.82	$29.82	$29.80	$29.80
Purchase #4	$118.93	7.238%	$127.5382	$127.54	$127.55	$127.50
Purchase #5	$132.41	11.625%	$147.8027	$147.80	$147.80	$147.80
Purchase #6	$160.40	7.139%	$171.851	$171.85	$171.85	$171.90
Purchase #7	$47.93	4.734%	$50.199	$50.20	$50.20	$50.20
7 purchase totals =	$861.81		$947.7430	$947.74	$947.75	$947.70