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	$135.89	5.345%	$143.1533	$143.15	$143.15	$143.20
Purchase #2	$27.48	11.171%	$30.5498	$30.55	$30.55	$30.50
Purchase #3	$96.78	13.237%	$109.5908	$109.59	$109.60	$109.60
Purchase #4	$206.87	7.766%	$222.9355	$222.94	$222.95	$222.90
Purchase #5	$21.31	12.351%	$23.942	$23.94	$23.95	$23.90
Purchase #6	$158.79	5.399%	$167.3631	$167.36	$167.35	$167.40
Purchase #7	$164.39	9.238%	$179.5763	$179.58	$179.60	$179.60
7 purchase totals =	$811.51		$877.1108	$877.11	$877.15	$877.10