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	$54.38	9.807%	$59.713	$59.71	$59.70	$59.70
Purchase #2	$132.43	8.333%	$143.4654	$143.47	$143.45	$143.50
Purchase #3	$103.51	9.783%	$113.6364	$113.64	$113.65	$113.60
Purchase #4	$168.96	6.279%	$179.569	$179.57	$179.55	$179.60
Purchase #5	$36.36	6.424%	$38.6958	$38.70	$38.70	$38.70
Purchase #6	$35.63	10.641%	$39.4214	$39.42	$39.40	$39.40
Purchase #7	$80.94	11.617%	$90.3428	$90.34	$90.35	$90.30
7 purchase totals =	$612.21		$664.8438	$664.85	$664.80	$664.80